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Advanced Form Management
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d="M747.1,121.1V79.3c0-15.8-9.4-22.4-26.6-22.4c-15,0-26.8,6.6-26.8,19.3c0,2.4,0.2,3.3,0.8,5h16.6 c-0.5-2-0.7-5-0.7-7.5c0-9.6,3.6-12.4,9.4-12.4c6.4,0,9.7,2,9.7,14.4v11.2l-20.8,7.7c-10.6,4.1-19.3,8.8-19.3,20.7 c0,10.9,7.5,17.8,18.6,17.8c9.9,0,17.4-6.2,21.9-12.1v-0.1h0.1l0,11.1l26,0.1v-4.5C749.3,127.1,747.1,126.2,747.1,121.1z M729.6,117.8c-4.4,3.3-7.6,5.3-12.1,5.4c-7.7,0-11.2-5.2-11.2-12.6c0-7.7,3.6-11.2,9.8-13.5l13.4-5.4L729.6,117.8L729.6,117.8z"
></path>
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d="M0,0v90.4c0,65.7,50.9,88.5,88.1,105.2h0.1l3,1.4c0.7-0.4,1.4-0.7,2.2-1c0.4-0.2,0.9-0.4,1.3-0.6 c37.3-16.6,88.4-39.5,88.4-105V0H0z M116,132l-2-5.3l-26.6-70c-1.6,4.1-5.3,14-9.3,24.6l-15.3,41.3c-0.7,2-0.3,3,0.2,3.7 c1.1,1.3,3.5,1.3,7.3,1.3H71l0,4.4H42.4l0-4.4h2.2c3.9,0,7.1-1.7,9.5-6.5l2.9-6.6l26.5-67.8l-4.7-12.5h24.7l34.1,89.7l3.1,8.1H116z"
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<h4 class="bd-toc-link">Web Applications I</h4>
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1. Applied JavaScript
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React Components and Component State
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Composing React Components and Passing Data Via Props
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Component Side Effects
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Advanced Styling Techniques
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Form Management
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Advanced Form Management
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<li class="toc-entry toc-h2"><a href="#prepare">Prepare</a></li>
<li class="toc-entry toc-h2"><a href="#learn">Learn</a></li>
<li class="toc-entry toc-h2"><a href="#project">Project</a></li>
<li class="toc-entry toc-h2"><a href="#review">Review</a></li>
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<h1 class="bd-title" id="content">
Advanced Form Management
</h1>
<span class="lead">
<p class="bd-lead"></p>
</span>
<strong
>At the end of this module, you should be able to:</strong
>
<ul>
<li>
control forms and form inputs (checkbox, dropdown) in
custom forms
</li>
<li>validate user input in forms</li>
<li>
make POST requests to pass data collected from a form to a
database
</li>
</ul>
</div>
<div class="alert alert-warning" role="alert">
<h4>Pro Tip</h4>
<p>
The first 90 percent of the code accounts for the first 90
percent of the development time. The remaining 10 percent of
the code accounts for the other 90 percent of the
development time.
</p>
<footer class="blockquote-footer">
<p>Tom Cargill, Bell Labs</p>
</footer>
</div>
<h2 class="display-4">
<a
id="prepare"
class="anchor"
href="#prepare"
aria-hidden="true"
><span class="octicon octicon-link"></span></a
>Prepare
</h2>
<p class="lead">Review each preclass resource before class.</p>
<div class="preclass">
<ul class="list-group list-group-flush"></ul>
</div>
<h2 class="display-4">
<a id="learn" class="anchor" href="#learn" aria-hidden="true"
><span class="octicon octicon-link"></span></a
>Learn
</h2>
<h4 class="mark mb-3 p-2">
Learn to control forms and form inputs (checkbox, dropdown) in
custom forms
</h4>
<p>
Forms can have many types of inputs, including: radio buttons,
check boxes, passwords, file uploads, and more. We want to be
able to include all types of inputs in forms to ensure we’re
collecting the best data possible.
</p>
<h5>Overview</h5>
<p>
Until this point we’ve been working primarily with text
inputs. Of course, forms can have many types of inputs,
including: radio buttons, check boxes, passwords, file
uploads, and more. You can view a full list of form input
types
<a
href="https://www.w3schools.com/html/html_form_input_types.asp"
>here</a
>.
</p>
<p>
Some of input types provide an additional challenge when
trying to control forms.
</p>
<h3 id="checkboxes">Checkboxes</h3>
<h4 id="set-default">Set-default</h4>
<p>
Just like with text inputs you can change the default values
of checkboxes from not checked to
<code class="highlighter-rouge">checked</code>. Similarly you
can specify a value that
</p>
<p>
In the example below the box would be checked by default like
so:
<input
type="checkbox"
name="nameOfChoice"
value="1"
checked
/>
</p>
<div class="language-js highlighter-rouge">
<div class="highlight">
<pre
class="highlight"
><code><span class="o"><</span><span class="nx">input</span> <span class="nx">type</span><span class="o">=</span><span class="dl">"</span><span class="s2">checkbox</span><span class="dl">"</span> <span class="nx">name</span><span class="o">=</span><span class="dl">"</span><span class="s2">nameOfChoice</span><span class="dl">"</span> <span class="nx">value</span><span class="o">=</span><span class="dl">"</span><span class="s2">1</span><span class="dl">"</span> <span class="nx">checked</span><span class="o">></span>
</code></pre>
</div>
</div>
<p>
Without the
<code class="highlighter-rouge">checked</code> argument, it
would look more like this:
<input type="checkbox" name="nameOfChoice" value="yes" />
</p>
<div class="language-js highlighter-rouge">
<div class="highlight">
<pre
class="highlight"
><code><span class="o"><</span><span class="nx">input</span> <span class="nx">type</span><span class="o">=</span><span class="dl">"</span><span class="s2">checkbox</span><span class="dl">"</span> <span class="nx">name</span><span class="o">=</span><span class="dl">"</span><span class="s2">nameOfChoice</span><span class="dl">"</span> <span class="nx">value</span><span class="o">=</span><span class="dl">"</span><span class="s2">yes</span><span class="dl">"</span><span class="o">></span>
</code></pre>
</div>
</div>
<p>
Here we also changed the value from the number
<code class="highlighter-rouge">1</code> to the string
<code class="highlighter-rouge">yes</code>, but that doesn’t
actually change anything for the user, it simply specifies
what should be added to the form object.
</p>
<h4 id="control-inputs">Control Inputs</h4>
<p>
That brings us to our next point, controlling inputs.
Controlling inputs for checkboxes, buttons, and other non-text
fields can be funky. If you want non-default values when a
field is checked you need to specify them in form setup and
this often requires some additional logic.
</p>
<p>
The following example would create a checkbox that, when
checked, would equal
<code class="highlighter-rouge">true</code> and would
<code class="highlighter-rouge">handleInputChange</code> like
you learned earlier. We will learn to control the state when
we talk about form validation.
</p>
<div class="language-js highlighter-rouge">
<div class="highlight">
<pre
class="highlight"
><code><span class="o"><</span><span class="nx">label</span><span class="o">></span>
<span class="nx">Check</span> <span class="nx">This</span> <span class="nx">Box</span><span class="p">:</span>
<span class="o"><</span><span class="nx">input</span>
<span class="nx">name</span><span class="o">=</span><span class="dl">"</span><span class="s2">isGoing</span><span class="dl">"</span>
<span class="nx">type</span><span class="o">=</span><span class="dl">"</span><span class="s2">checkbox</span><span class="dl">"</span>
<span class="nx">checked</span><span class="o">=</span><span class="p">{</span><span class="kc">true</span><span class="p">}</span>
<span class="nx">onChange</span><span class="o">=</span><span class="p">{</span><span class="nx">handleInputChange</span><span class="p">}</span> <span class="sr">/</span><span class="err">>
</span><span class="o"><</span><span class="sr">/label</span><span class="err">>
</span></code></pre>
</div>
</div>
<h3 id="dropdown">Dropdown</h3>
<p>
Dropdown menus are really important for gathering mass data
because they insure data quality. This is done with the
<code class="highlighter-rouge"><select></code> element.
Between the
<code class="highlighter-rouge"><select></code> tags,
you’ll place all of the options you want to have in the
dropdown menu.
</p>
<div class="language-js highlighter-rouge">
<div class="highlight">
<pre
class="highlight"
><code><span class="o"><</span><span class="nx">form</span><span class="o">></span>
<span class="o"><</span><span class="nx">select</span> <span class="nx">id</span><span class="o">=</span><span class="dl">"</span><span class="s2">friends</span><span class="dl">"</span> <span class="nx">name</span><span class="o">=</span><span class="dl">"</span><span class="s2">friends</span><span class="dl">"</span><span class="o">></span>
<span class="o"><</span><span class="nx">option</span> <span class="nx">value</span><span class="o">=</span><span class="dl">"</span><span class="s2">Ross</span><span class="dl">"</span><span class="o">></span>
<span class="o"><</span><span class="nx">option</span> <span class="nx">value</span><span class="o">=</span><span class="dl">"</span><span class="s2">Rachel</span><span class="dl">"</span><span class="o">></span>
<span class="o"><</span><span class="nx">option</span> <span class="nx">value</span><span class="o">=</span><span class="dl">"</span><span class="s2">Monica</span><span class="dl">"</span><span class="o">></span>
<span class="o"><</span><span class="nx">option</span> <span class="nx">value</span><span class="o">=</span><span class="dl">"</span><span class="s2">Phoebe</span><span class="dl">"</span><span class="o">></span>
<span class="o"><</span><span class="nx">option</span> <span class="nx">value</span><span class="o">=</span><span class="dl">"</span><span class="s2">Chandler</span><span class="dl">"</span><span class="o">></span>
<span class="o"><</span><span class="nx">option</span> <span class="nx">value</span><span class="o">=</span><span class="dl">"</span><span class="s2">Joey</span><span class="dl">"</span><span class="o">></span>
<span class="o"><</span><span class="sr">/select</span><span class="err">>
</span><span class="o"><</span><span class="sr">/form</span><span class="err">>
</span></code></pre>
</div>
</div>
<h5>Follow Along</h5>
<p>
Let’s build out a form to gather user information with radio
buttons, a checklist, and a dropdown. These are some common
data types you might work with in your time as a web
developer.
</p>
<ol>
<li>
<strong>Set up form.</strong> Using our knowledge from the
“form management” module, we’ll first set up a basic form
with a single text input, Name.
</li>
</ol>
<div class="language-js highlighter-rouge">
<div class="highlight">
<pre
class="highlight"
><code> <span class="k">return</span> <span class="p">(</span>
<span class="o"><</span><span class="nx">div</span> <span class="nx">className</span><span class="o">=</span><span class="dl">"</span><span class="s2">App</span><span class="dl">"</span><span class="o">></span>
<span class="p">{</span><span class="nx">console</span><span class="p">.</span><span class="nx">log</span><span class="p">(</span><span class="nx">name</span><span class="p">)}</span>
<span class="o"><</span><span class="nx">form</span><span class="o">></span>
<span class="o"><</span><span class="nx">label</span><span class="o">></span>
<span class="nx">Name</span><span class="p">:</span>
<span class="o"><</span><span class="nx">input</span> <span class="nx">type</span><span class="o">=</span><span class="dl">"</span><span class="s2">text</span><span class="dl">"</span> <span class="nx">onChange</span><span class="o">=</span><span class="p">{</span><span class="nx">event</span> <span class="o">=></span> <span class="nx">handleChange</span><span class="p">(</span><span class="nx">event</span><span class="p">)}</span> <span class="sr">/</span><span class="err">>
</span> <span class="o"><</span><span class="sr">/label</span><span class="err">>
</span> <span class="o"><</span><span class="nx">button</span> <span class="nx">onSubmit</span><span class="o">=</span><span class="p">{()</span> <span class="o">=></span> <span class="nx">handleSubmit</span><span class="p">()}</span><span class="o">></span><span class="nx">Submit</span><span class="o">!<</span><span class="sr">/button</span><span class="err">>
</span> <span class="o"><</span><span class="sr">/form</span><span class="err">>
</span> <span class="o"><</span><span class="sr">/div</span><span class="err">>
</span> <span class="p">);</span>
<span class="p">}</span>
<span class="k">export</span> <span class="k">default</span> <span class="nx">App</span><span class="p">;</span>
</code></pre>
</div>
</div>
<ol>
<li>
<strong>Add Radio Buttons</strong>. Next, we’ll add radio
buttons. If we wanted to gather categorical data, like an
age range, we might use radio buttons. To make radio buttons
all we need to do is add
<code class="highlighter-rouge">input</code> elements with
the type <code class="highlighter-rouge">"radio"</code>.
These are, by default, inline elements, so they’ll render
nicely in a row.
</li>
</ol>
<div class="language-js highlighter-rouge">
<div class="highlight">
<pre
class="highlight"
><code> <span class="o"><</span><span class="nx">p</span><span class="o">></span> <span class="nx">Age</span> <span class="nx">Range</span><span class="p">:</span> <span class="o"><</span><span class="sr">/p</span><span class="err">>
</span> <span class="o"><</span><span class="nx">label</span><span class="o">></span>
<span class="mi">13</span><span class="o">-</span><span class="mi">18</span>
<span class="o"><</span><span class="nx">input</span> <span class="nx">type</span><span class="o">=</span><span class="dl">"</span><span class="s2">radio</span><span class="dl">"</span> <span class="nx">onChange</span><span class="o">=</span><span class="p">{</span><span class="nx">event</span> <span class="o">=></span> <span class="nx">handleChange</span><span class="p">(</span><span class="nx">event</span><span class="p">)}</span> <span class="sr">/</span><span class="err">>
</span> <span class="mi">19</span><span class="o">-</span><span class="mi">24</span>
<span class="o"><</span><span class="nx">input</span> <span class="nx">type</span><span class="o">=</span><span class="dl">"</span><span class="s2">radio</span><span class="dl">"</span> <span class="nx">onChange</span><span class="o">=</span><span class="p">{</span><span class="nx">event</span> <span class="o">=></span> <span class="nx">handleChange</span><span class="p">(</span><span class="nx">event</span><span class="p">)}</span> <span class="sr">/</span><span class="err">>
</span> <span class="mi">25</span><span class="o">-</span><span class="mi">39</span>
<span class="o"><</span><span class="nx">input</span> <span class="nx">type</span><span class="o">=</span><span class="dl">"</span><span class="s2">radio</span><span class="dl">"</span> <span class="nx">onChange</span><span class="o">=</span><span class="p">{</span><span class="nx">event</span> <span class="o">=></span> <span class="nx">handleChange</span><span class="p">(</span><span class="nx">event</span><span class="p">)}</span> <span class="sr">/</span><span class="err">>
</span> <span class="mi">40</span><span class="o">+</span>
<span class="o"><</span><span class="nx">input</span> <span class="nx">type</span><span class="o">=</span><span class="dl">"</span><span class="s2">radio</span><span class="dl">"</span> <span class="nx">onChange</span><span class="o">=</span><span class="p">{</span><span class="nx">event</span> <span class="o">=></span> <span class="nx">handleChange</span><span class="p">(</span><span class="nx">event</span><span class="p">)}</span> <span class="sr">/</span><span class="err">>
</span> <span class="o"><</span><span class="sr">/label</span><span class="err">>
</span></code></pre>
</div>
</div>
<ol>
<li>
<strong>Add Dropdown</strong>. Another way to gather
categorical data is through a dropdown. Let’s add one here
to ask which state the user lives in. For illustration
purposes, we’ll only add 5 states, but you could easily use
an array and
<code class="highlighter-rouge">.map</code> method to add
all 50 states.
</li>
</ol>
<div class="language-js highlighter-rouge">
<div class="highlight">
<pre
class="highlight"
><code><span class="o"><</span><span class="nx">form</span><span class="o">></span>
<span class="o"><</span><span class="nx">select</span> <span class="nx">id</span><span class="o">=</span><span class="dl">"</span><span class="s2">states</span><span class="dl">"</span> <span class="nx">name</span><span class="o">=</span><span class="dl">"</span><span class="s2">states>
<option value=</span><span class="dl">"</span><span class="nx">Alabama</span><span class="dl">"</span><span class="s2"> />
<option value=</span><span class="dl">"</span><span class="nx">Alaska</span><span class="dl">"</span><span class="s2"> />
<option value=</span><span class="dl">"</span><span class="nx">Arizona</span><span class="dl">"</span><span class="s2"> />
<option value=</span><span class="dl">"</span><span class="nx">Arkansas</span><span class="dl">"</span><span class="s2"> />
<option value=</span><span class="dl">"</span><span class="nx">Colorado</span><span class="dl">"</span><span class="s2"> />
</select>
</form>
</span></code></pre>
</div>
</div>
<ol>
<li>
<strong>Add a checklist.</strong> Last but not least let’s
play around with a checklist. Checklists are a great way to
gather boolean data. For these we simply change the input
value to <code class="highlighter-rouge">"checkbox"</code>.
We also need to consider what a check means and set up our
form accordingly. In the example below, when the box is
checked we update the state of “RSVP” to “yes”,
</li>
</ol>
<div class="language-js highlighter-rouge">
<div class="highlight">
<pre
class="highlight"
><code><span class="o"><</span><span class="nx">label</span><span class="o">></span>
<span class="nx">RSVP</span><span class="p">:</span>
<span class="o"><</span><span class="nx">input</span>
<span class="nx">name</span><span class="o">=</span><span class="dl">"</span><span class="s2">isGoing</span><span class="dl">"</span>
<span class="nx">type</span><span class="o">=</span><span class="dl">"</span><span class="s2">checkbox</span><span class="dl">"</span>
<span class="nx">checked</span><span class="o">=</span><span class="p">{</span><span class="kc">false</span><span class="p">}</span>
<span class="nx">onChange</span><span class="o">=</span><span class="p">{</span><span class="nx">handleInputChange</span><span class="p">}</span> <span class="sr">/</span><span class="err">>
</span><span class="o"><</span><span class="sr">/label</span><span class="err">>
</span></code></pre>
</div>
</div>
<h5>Challenge</h5>
<p>
Add a non-text field to a project from the form management
lessons.
</p>
<hr />
<h4 class="mark mb-3 p-2">
Learn to validate user input in forms
</h4>
<p>
As our users start typing into our beautiful form we’ve
created, they will very often type in the wrong data into the
wrong field. Or maybe they will not format the data correctly
(think setting up strong passwords, or even typing in a phone
number or email). We want to give our users the best user
experience by giving them informed feedback when they’ve
filled out our form incorrectly. This is done with form
validation.
</p>
<h5>Overview</h5>
<p>
You know when you try to make your password “password” and the
form tells you to chose a stronger password? That’s called
validation. There are many ways to validate input before you
submit the form to a server or other service and they’re all
really useful for insuring the quality of data.
</p>
<p>
One common strategy is to compare the input string to a
regular expression model of expected characters and handle the
input based on the results of the comparison.
</p>
<p>
Another popular method is to have a library such as
<code class="highlighter-rouge">Yup</code> handle the
validation for us - yup has built in methods to deal with
email addresses, passwords, strings, numbers, and more. You
can read the full documentation
<a href="https://github.com/jquense/yup">here</a>.
</p>
<h3 id="validating-a-string">Validating a String</h3>
<p>
Before we move into the follow along tutorial, lets look at
how we could use Yup to validate if an input was a string.
This is in a lot of ways the “Hello World” of form validation.
</p>
<p>
First, you’ll need to install yup with
<code class="highlighter-rouge">npm install --save yup</code>.
</p>
<p>
Then, we simply declare a schema with
<code class="highlighter-rouge"
>let schema = yup.string();</code
>
and test our schema on a new line with
<code class="highlighter-rouge"
>await schema.isValid('hello world');</code
>. This would return “true” since ‘hello world’ is a string.
</p>
<h3 id="validating-a-form">Validating a Form</h3>
<p>
Form validation is slightly more complicated but it follows
the same logical pattern. First we declare a schema, then we
validate data.
</p>
<p>
In a forms app, the schema defines what the form looks like.
It is kind of like a form outline, telling yup what the
existing fields are and how they should be validated. We’ll
walk through this process below.
</p>
<p>
You can always chose to use additional helper libraries, like
Formik, to validate forms, but for learning purposes it is
best to understand the validation process with just Yup.
</p>
<h5>Follow Along</h5>
<p>
We’ll start with a Yup login form consisting of an email and
password field.
</p>
<div class="language-js highlighter-rouge">
<div class="highlight">
<pre
class="highlight"
><code><span class="k">import</span> <span class="nx">React</span> <span class="k">from</span> <span class="dl">"</span><span class="s2">react</span><span class="dl">"</span><span class="p">;</span>
<span class="c1">// Basic submit event handler and console.log to confirm form submitted</span>
<span class="kd">const</span> <span class="nx">formSubmit</span> <span class="o">=</span> <span class="nx">e</span> <span class="o">=></span> <span class="p">{</span>
<span class="nx">e</span><span class="p">.</span><span class="nx">preventDefault</span><span class="p">();</span>
<span class="nx">console</span><span class="p">.</span><span class="nx">log</span><span class="p">(</span><span class="dl">"</span><span class="s2">submitted</span><span class="dl">"</span><span class="p">);</span>
<span class="p">};</span>
<span class="c1">// Create state for the form values. We will want to update state later on, but for now... empty strings!</span>
<span class="kd">const</span> <span class="p">[</span><span class="nx">formState</span><span class="p">,</span> <span class="nx">setFormState</span><span class="p">]</span> <span class="o">=</span> <span class="nx">useState</span><span class="p">({</span>
<span class="na">name</span><span class="p">:</span> <span class="dl">""</span><span class="p">,</span>
<span class="na">email</span><span class="p">:</span> <span class="dl">""</span><span class="p">,</span>
<span class="na">website</span><span class="p">:</span> <span class="dl">""</span><span class="p">,</span>
<span class="na">password</span><span class="p">:</span> <span class="dl">""</span>
<span class="p">});</span>
<span class="c1">// Define form elements: email, password and terms/conditions</span>
<span class="kd">function</span> <span class="nx">LoginForm</span><span class="p">()</span> <span class="p">{</span>
<span class="k">return</span> <span class="p">(</span>
<span class="o"><</span><span class="nx">form</span><span class="o">></span>
<span class="o"><</span><span class="nx">label</span> <span class="nx">htmlFor</span><span class="o">=</span><span class="dl">"</span><span class="s2">emailInput</span><span class="dl">"</span><span class="o">></span>
<span class="nx">Name</span>
<span class="o"><</span><span class="nx">input</span> <span class="nx">id</span><span class="o">=</span><span class="dl">"</span><span class="s2">emailInput</span><span class="dl">"</span> <span class="nx">type</span><span class="o">=</span><span class="dl">"</span><span class="s2">email</span><span class="dl">"</span> <span class="nx">name</span><span class="o">=</span><span class="dl">"</span><span class="s2">email</span><span class="dl">"</span> <span class="nx">placeholder</span><span class="o">=</span><span class="dl">"</span><span class="s2">Email</span><span class="dl">"</span> <span class="o">/></span>
<span class="o"><</span><span class="sr">/label</span><span class="err">>
</span> <span class="o"><</span><span class="nx">label</span> <span class="nx">htmlFor</span><span class="o">=</span><span class="dl">"</span><span class="s2">passwordInput</span><span class="dl">"</span><span class="o">></span>
<span class="nx">Password</span>
<span class="o"><</span><span class="nx">input</span> <span class="nx">id</span><span class="o">=</span><span class="dl">"</span><span class="s2">passwordInput</span><span class="dl">"</span> <span class="nx">type</span><span class="o">=</span><span class="dl">"</span><span class="s2">password</span><span class="dl">"</span> <span class="nx">name</span><span class="o">=</span><span class="dl">"</span><span class="s2">password</span><span class="dl">"</span> <span class="nx">placeholder</span><span class="o">=</span><span class="dl">"</span><span class="s2">Password</span><span class="dl">"</span> <span class="o">/></span>
<span class="o"><</span><span class="sr">/label</span><span class="err">>
</span> <span class="o"><</span><span class="nx">label</span> <span class="nx">htmlFor</span><span class="o">=</span><span class="dl">"</span><span class="s2">termsInput</span><span class="dl">"</span><span class="o">></span>
<span class="nx">Do</span> <span class="nx">you</span> <span class="nx">agree</span> <span class="nx">to</span> <span class="nx">the</span> <span class="nx">terms</span> <span class="nx">and</span> <span class="nx">conditions</span><span class="p">?</span>
<span class="o"><</span><span class="nx">input</span> <span class="nx">id</span><span class="o">=</span><span class="dl">"</span><span class="s2">termsInput</span><span class="dl">"</span> <span class="nx">type</span><span class="o">=</span><span class="dl">"</span><span class="s2">checkbox</span><span class="dl">"</span> <span class="nx">name</span><span class="o">=</span><span class="dl">"</span><span class="s2">terms</span><span class="dl">"</span> <span class="o">/></span>
<span class="o"><</span><span class="sr">/label</span><span class="err">>
</span> <span class="o"><</span><span class="nx">button</span><span class="o">></span><span class="nx">Submit</span><span class="o">!<</span><span class="sr">/button</span><span class="err">>
</span> <span class="o"><</span><span class="sr">/form</span><span class="err">>
</span> <span class="p">);</span>
</code></pre>
</div>
</div>
<p>
To start the validation process, add Yup as a dependency and
import it into the component file. In the command line we’ll
type:
</p>
<div class="language-bash highlighter-rouge">
<div class="highlight">
<pre
class="highlight"
><code>npm <span class="nb">install</span> <span class="nt">--save</span> yup
</code></pre>
</div>
</div>
<p>and in our file:</p>
<div class="language-js highlighter-rouge">
<div class="highlight">
<pre
class="highlight"
><code><span class="k">import</span> <span class="o">*</span> <span class="k">as</span> <span class="nx">Yup</span> <span class="k">from</span> <span class="dl">"</span><span class="s2">yup</span><span class="dl">"</span><span class="p">;</span>
<span class="c1">// You may see this as (import Yup from 'yup') in some tutorials, the above method seems less buggy</span>
</code></pre>
</div>
</div>
<p>
Next we will define our schema - which is basically a
description of what each named field is supposed to look like
so that Yup can pass or fail the input. Give it a shape of all
the elements in your form. Depending on what you’re trying to
validate you give it strings, checkboxes, etc. That might look
like so:
</p>
<div class="language-js highlighter-rouge">
<div class="highlight">
<pre
class="highlight"
><code><span class="kd">const</span> <span class="nx">formSchema</span> <span class="o">=</span> <span class="nx">Yup</span><span class="p">.</span><span class="nx">object</span><span class="p">().</span><span class="nx">shape</span><span class="p">({</span>
<span class="na">email</span><span class="p">:</span> <span class="nx">Yup</span>
<span class="p">.</span><span class="nx">string</span><span class="p">()</span>
<span class="p">.</span><span class="nx">email</span><span class="p">(</span><span class="dl">"</span><span class="s2">Must be a valid email address.</span><span class="dl">"</span><span class="p">)</span>
<span class="p">.</span><span class="nx">required</span><span class="p">(</span><span class="dl">"</span><span class="s2">Must include email address.</span><span class="dl">"</span><span class="p">),</span>
<span class="na">password</span><span class="p">:</span> <span class="nx">Yup</span>
<span class="p">.</span><span class="nx">string</span><span class="p">()</span>
<span class="p">.</span><span class="nx">min</span><span class="p">(</span><span class="mi">6</span><span class="p">,</span> <span class="dl">"</span><span class="s2">Passwords must be at least 6 characters long.</span><span class="dl">"</span><span class="p">)</span>
<span class="p">.</span><span class="nx">required</span><span class="p">(</span><span class="dl">"</span><span class="s2">Password is Required</span><span class="dl">"</span><span class="p">)</span>
<span class="na">terms</span><span class="p">:</span> <span class="nx">Yup</span>
<span class="p">.</span><span class="nx">boolean</span><span class="p">()</span>
<span class="p">.</span><span class="nx">oneOf</span><span class="p">([</span><span class="kc">true</span><span class="p">],</span> <span class="dl">"</span><span class="s2">You must accept Terms and Conditions</span><span class="dl">"</span><span class="p">)</span>
<span class="c1">// required isn't required for checkboxes.</span>
<span class="p">});</span>
</code></pre>
</div>
</div>
<p>
The <code class="highlighter-rouge">formSchema</code> is a lot
like a
<code class="highlighter-rouge">propType</code> definition
because you need to tell Yup what shape the data is supposed
to take.
</p>
<p>
The customization part is pretty straightforward. For the
<code class="highlighter-rouge">email</code> field, Yup is
looking for a string that looks like an email-pattern, and you
need to have this field (it’s
<code class="highlighter-rouge">required</code>).
</p>
<p>
The <code class="highlighter-rouge">password</code> schema
shows that you expect a string with a minimum of 6 characters.
Additionally, the user shouldn’t be able to submit the form
without a password.
</p>
<p>
There are tons of options available in a schema. Look up how
to use this powerful tool
<a href="https://github.com/jquense/yup">here</a>.
</p>
<p>
Next up, we’ll create state for the form values. Just like
earlier, this is the initial state values for each input in
the form.
</p>
<p>Next up, state for error messages.</p>
<div class="language-js highlighter-rouge">
<div class="highlight">
<pre
class="highlight"
><code> <span class="c1">// State for the error messages</span>
<span class="kd">const</span> <span class="p">[</span><span class="nx">errors</span><span class="p">,</span> <span class="nx">setErrors</span><span class="p">]</span> <span class="o">=</span> <span class="nx">useState</span><span class="p">({</span>
<span class="na">email</span><span class="p">:</span> <span class="dl">""</span><span class="p">,</span>
<span class="na">password</span><span class="p">:</span> <span class="dl">""</span><span class="p">,</span>
<span class="na">terms</span><span class="p">:</span> <span class="dl">""</span>
<span class="p">});</span>
</code></pre>
</div>
</div>
<p>
We’re going to change the state of the button so that when
we’re filling out the form it won’t be able to submit until
the validation passes. The forms will submit even if the
validation is failing, we’re using the button’s state to
disable the button. Ultimately though, the form state still
controls wither or not the form can be submitted.
</p>
<div class="language-js highlighter-rouge">
<div class="highlight">
<pre
class="highlight"
><code> <span class="cm">/* Each time the form value state is updated, check to see if it is valid per our schema.
This will allow us to enable/disable the submit button.*/</span>
<span class="nx">useEffect</span><span class="p">(()</span> <span class="o">=></span> <span class="p">{</span>
<span class="cm">/* We pass the entire state into the entire schema, no need to use reach here.
We want to make sure it is all valid before we allow a user to submit
isValid comes from Yup directly */</span>
<span class="nx">formSchema</span><span class="p">.</span><span class="nx">isValid</span><span class="p">(</span><span class="nx">formState</span><span class="p">).</span><span class="nx">then</span><span class="p">(</span><span class="nx">valid</span> <span class="o">=></span> <span class="p">{</span>
<span class="nx">setButtonDisabled</span><span class="p">(</span><span class="o">!</span><span class="nx">valid</span><span class="p">);</span>
<span class="p">});</span>
<span class="p">},</span> <span class="p">[</span><span class="nx">formState</span><span class="p">]);</span>
</code></pre>
</div>
</div>
<p>
The last thing we need to do before validating the form is set
up an event handler called
<code class="highlighter-rouge">inputChange</code> and pass in
the event parameter. React uses it’s own event system (known
as a “synthetic event”). These events are meant to look like
normal DOM events, and in the majority of cases we can use
them in the same way. However, there are some small
inconsistencies. One of those differences is the fact that we
can not use the React event object in an asynchronous way on
its own. If you plan on using the event object in a callback
or a promise resolution you will need to call
<code class="highlighter-rouge">.persist()</code> on your
event object before you use it. If you are interested in
learning more about why this is the case (it’s actually