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<!DOCTYPE html>
<html>
<head>
<title>Readme</title>
<meta charset="utf-8" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<link
rel="stylesheet"
href="file:///c:\Users\PACE\.vscode\extensions\shd101wyy.markdown-preview-enhanced-0.6.8\node_modules\@shd101wyy\mume\dependencies\katex\katex.min.css" />
<style>
/**
* prism.js Github theme based on GitHub's theme.
* @author Sam Clarke
*/
code[class*="language-"],
pre[class*="language-"] {
color: #333;
background: none;
font-family: Consolas, "Liberation Mono", Menlo, Courier, monospace;
text-align: left;
white-space: pre;
word-spacing: normal;
word-break: normal;
word-wrap: normal;
line-height: 1.4;
-moz-tab-size: 8;
-o-tab-size: 8;
tab-size: 8;
-webkit-hyphens: none;
-moz-hyphens: none;
-ms-hyphens: none;
hyphens: none;
}
/* Code blocks */
pre[class*="language-"] {
padding: 0.8em;
overflow: auto;
/* border: 1px solid #ddd; */
border-radius: 3px;
/* background: #fff; */
background: #f5f5f5;
}
/* Inline code */
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padding: 0.1em;
border-radius: 0.3em;
white-space: normal;
background: #f5f5f5;
}
.token.comment,
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color: #969896;
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color: #183691;
}
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.token.punctuation,
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color: #333;
}
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color: #a71d5d;
}
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color: #183691;
}
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.token.number,
.token.boolean,
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color: #0086b3;
}
.token.tag,
.token.selector,
.token.prolog {
color: #63a35c;
}
.token.function,
.token.namespace,
.token.pseudo-element,
.token.class,
.token.class-name,
.token.pseudo-class,
.token.id,
.token.url-reference .token.variable,
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color: #795da3;
}
.token.entity {
cursor: help;
}
.token.title,
.token.title .token.punctuation {
font-weight: bold;
color: #1d3e81;
}
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color: #ed6a43;
}
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background-color: #eaffea;
color: #55a532;
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background-color: #ffecec;
color: #bd2c00;
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font-weight: bold;
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font-style: italic;
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/* JSON */
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color: #183691;
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color: #333;
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/* CSS */
code.language-css,
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color: #0086b3;
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/* YAML */
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color: #63a35c;
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code.language-yaml {
color: #183691;
}
/* Ruby */
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color: #333;
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/* Markdown */
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color: #795da3;
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color: #795da3;
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color: #183691;
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color: #0086b3;
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color: #0086b3;
}
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position: relative;
padding: 1em 0 1em 3em;
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left: 0;
background-color: transparent;
display: block;
width: 100%;
}
pre[data-line] .line-highlight {
position: absolute;
left: 0;
right: 0;
padding: inherit 0;
margin-top: 1em;
background: hsla(24, 20%, 50%, 0.08);
background: linear-gradient(
to right,
hsla(24, 20%, 50%, 0.1) 70%,
hsla(24, 20%, 50%, 0)
);
pointer-events: none;
line-height: inherit;
white-space: pre;
}
pre[data-line] .line-highlight:before,
pre[data-line] .line-highlight[data-end]:after {
content: attr(data-start);
position: absolute;
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left: 0.6em;
min-width: 1em;
padding: 0 0.5em;
background-color: hsla(24, 20%, 50%, 0.4);
color: hsl(24, 20%, 95%);
font: bold 65%/1.5 sans-serif;
text-align: center;
vertical-align: 0.3em;
border-radius: 999px;
text-shadow: none;
box-shadow: 0 1px white;
}
pre[data-line] .line-highlight[data-end]:after {
content: attr(data-end);
top: auto;
bottom: 0.4em;
}
html body {
font-family: "Helvetica Neue", Helvetica, "Segoe UI", Arial, freesans,
sans-serif;
font-size: 16px;
line-height: 1.6;
color: #333;
background-color: #fff;
overflow: initial;
box-sizing: border-box;
word-wrap: break-word;
}
html body > :first-child {
margin-top: 0;
}
html body h1,
html body h2,
html body h3,
html body h4,
html body h5,
html body h6 {
line-height: 1.2;
margin-top: 1em;
margin-bottom: 16px;
color: #000;
}
html body h1 {
font-size: 2.25em;
font-weight: 300;
padding-bottom: 0.3em;
}
html body h2 {
font-size: 1.75em;
font-weight: 400;
padding-bottom: 0.3em;
}
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html body h6 {
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font-weight: 600;
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html body h1,
html body h2,
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html body h4,
html body h5 {
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html body h5 {
font-size: 1em;
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html body h6 {
color: #5c5c5c;
}
html body strong {
color: #000;
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html body del {
color: #5c5c5c;
}
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color: inherit;
text-decoration: none;
}
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text-decoration: none;
}
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color: #00a3f5;
text-decoration: none;
}
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max-width: 100%;
}
html body > p {
margin-top: 0;
margin-bottom: 16px;
word-wrap: break-word;
}
html body > ul,
html body > ol {
margin-bottom: 16px;
}
html body ul,
html body ol {
padding-left: 2em;
}
html body ul.no-list,
html body ol.no-list {
padding: 0;
list-style-type: none;
}
html body ul ul,
html body ul ol,
html body ol ol,
html body ol ul {
margin-top: 0;
margin-bottom: 0;
}
html body li {
margin-bottom: 0;
}
html body li.task-list-item {
list-style: none;
}
html body li > p {
margin-top: 0;
margin-bottom: 0;
}
html body .task-list-item-checkbox {
margin: 0 0.2em 0.25em -1.8em;
vertical-align: middle;
}
html body .task-list-item-checkbox:hover {
cursor: pointer;
}
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margin: 16px 0;
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padding: 0 15px;
color: #5c5c5c;
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border-left: 4px solid #d6d6d6;
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html body blockquote > :first-child {
margin-top: 0;
}
html body blockquote > :last-child {
margin-bottom: 0;
}
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height: 4px;
margin: 32px 0;
background-color: #d6d6d6;
border: 0 none;
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html body table {
margin: 10px 0 15px 0;
border-collapse: collapse;
border-spacing: 0;
display: block;
width: 100%;
overflow: auto;
word-break: normal;
word-break: keep-all;
}
html body table th {
font-weight: bold;
color: #000;
}
html body table td,
html body table th {
border: 1px solid #d6d6d6;
padding: 6px 13px;
}
html body dl {
padding: 0;
}
html body dl dt {
padding: 0;
margin-top: 16px;
font-size: 1em;
font-style: italic;
font-weight: bold;
}
html body dl dd {
padding: 0 16px;
margin-bottom: 16px;
}
html body code {
font-family: Menlo, Monaco, Consolas, "Courier New", monospace;
font-size: 0.85em !important;
color: #000;
background-color: #f0f0f0;
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padding: 0.2em 0;
}
html body code::before,
html body code::after {
letter-spacing: -0.2em;
content: "\00a0";
}
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padding: 0;
margin: 0;
font-size: 0.85em !important;
word-break: normal;
white-space: pre;
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border: 0;
}
html body .highlight {
margin-bottom: 16px;
}
html body .highlight pre,
html body pre {
padding: 1em;
overflow: auto;
font-size: 0.85em !important;
line-height: 1.45;
border: #d6d6d6;
border-radius: 3px;
}
html body .highlight pre {
margin-bottom: 0;
word-break: normal;
}
html body pre code,
html body pre tt {
display: inline;
max-width: initial;
padding: 0;
margin: 0;
overflow: initial;
line-height: inherit;
word-wrap: normal;
background-color: transparent;
border: 0;
}
html body pre code:before,
html body pre tt:before,
html body pre code:after,
html body pre tt:after {
content: normal;
}
html body p,
html body blockquote,
html body ul,
html body ol,
html body dl,
html body pre {
margin-top: 0;
margin-bottom: 16px;
}
html body kbd {
color: #000;
border: 1px solid #d6d6d6;
border-bottom: 2px solid #c7c7c7;
padding: 2px 4px;
background-color: #f0f0f0;
border-radius: 3px;
}
@media print {
html body {
background-color: #fff;
}
html body h1,
html body h2,
html body h3,
html body h4,
html body h5,
html body h6 {
color: #000;
page-break-after: avoid;
}
html body blockquote {
color: #5c5c5c;
}
html body pre {
page-break-inside: avoid;
}
html body table {
display: table;
}
html body img {
display: block;
max-width: 100%;
max-height: 100%;
}
html body pre,
html body code {
word-wrap: break-word;
white-space: pre;
}
}
.markdown-preview {
width: 100%;
height: 100%;
box-sizing: border-box;
}
.markdown-preview .pagebreak,
.markdown-preview .newpage {
page-break-before: always;
}
.markdown-preview pre.line-numbers {
position: relative;
padding-left: 3.8em;
counter-reset: linenumber;
}
.markdown-preview pre.line-numbers > code {
position: relative;
}
.markdown-preview pre.line-numbers .line-numbers-rows {
position: absolute;
pointer-events: none;
top: 1em;
font-size: 100%;
left: 0;
width: 3em;
letter-spacing: -1px;
border-right: 1px solid #999;
-webkit-user-select: none;
-moz-user-select: none;
-ms-user-select: none;
user-select: none;
}
.markdown-preview pre.line-numbers .line-numbers-rows > span {
pointer-events: none;
display: block;
counter-increment: linenumber;
}
.markdown-preview pre.line-numbers .line-numbers-rows > span:before {
content: counter(linenumber);
color: #999;
display: block;
padding-right: 0.8em;
text-align: right;
}
.markdown-preview .mathjax-exps .MathJax_Display {
text-align: center !important;
}
.markdown-preview:not([for="preview"]) .code-chunk .btn-group {
display: none;
}
.markdown-preview:not([for="preview"]) .code-chunk .status {
display: none;
}
.markdown-preview:not([for="preview"]) .code-chunk .output-div {
margin-bottom: 16px;
}
.markdown-preview .md-toc {
padding: 0;
}
.markdown-preview .md-toc .md-toc-link-wrapper .md-toc-link {
display: inline;
padding: 0.25rem 0;
}
.markdown-preview .md-toc .md-toc-link-wrapper .md-toc-link p,
.markdown-preview .md-toc .md-toc-link-wrapper .md-toc-link div {
display: inline;
}
.markdown-preview .md-toc .md-toc-link-wrapper.highlighted .md-toc-link {
font-weight: 800;
}
.scrollbar-style::-webkit-scrollbar {
width: 8px;
}
.scrollbar-style::-webkit-scrollbar-track {
border-radius: 10px;
background-color: transparent;
}
.scrollbar-style::-webkit-scrollbar-thumb {
border-radius: 5px;
background-color: rgba(150, 150, 150, 0.66);
border: 4px solid rgba(150, 150, 150, 0.66);
background-clip: content-box;
}
html body[for="html-export"]:not([data-presentation-mode]) {
position: relative;
width: 100%;
height: 100%;
top: 0;
left: 0;
margin: 0;
padding: 0;
overflow: auto;
}
html
body[for="html-export"]:not([data-presentation-mode])
.markdown-preview {
position: relative;
top: 0;
}
@media screen and (min-width: 914px) {
html
body[for="html-export"]:not([data-presentation-mode])
.markdown-preview {
padding: 2em calc(50% - 457px + 2em);
}
}
@media screen and (max-width: 914px) {
html
body[for="html-export"]:not([data-presentation-mode])
.markdown-preview {
padding: 2em;
}
}
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/* Please visit the URL below for more information: */
/* https://shd101wyy.github.io/markdown-preview-enhanced/#/customize-css */
</style>
</head>
<body for="html-export">
<div class="mume markdown-preview">
<h1
class="mume-header"
id="33-javascript-concepts-every-developer-should-know-%EF%B8%8F%EF%B8%8Fhttpsgithubcomleonardomso33-js-concepts">
<a href="https://thewecas.github.io/JavaScript/"
>33 JavaScript Concepts Every Developer Should Know
🤓️💯️</a
>
</h1>
<p>Reference :</p>
<h3
class="mume-header"
id="33-js-conceptshttpsgithubcomleonardomso33-js-concepts-by-leonardo-maldonadohttpsgithubcomleonardomso-on-github">
<a href="https://github.com/leonardomso/33-js-concepts"
>33-js-concepts</a
>
by <a href="https://github.com/leonardomso">Leonardo Maldonado</a> on
Github
</h3>
<hr />
<h2
class="mume-header"
id="1-call-stack-heap-queue-execution-context-event-loop">
1. Call stack, Heap, Queue, Execution Context, Event Loop
</h2>
<ul>
<li>
<h3>Execution Context</h3>
<ul>
<li>Where Execution of code takes place</li>
<li>
it has 2 components
<ul>
<li>
Memory : where variables and functions are stored as key:value
pair
</li>
<li>Code : where execution of code happens</li>
</ul>
</li>
</ul>
</li>
<li>
<h3>Call Stack</h3>
<ul>
<li>Data structure for recording function calls</li>
<li>Max calls in chrome is 16,000 frames</li>
</ul>
</li>
<li>
<h3>Heap</h3>
<ul>
<li>Memory allocation to variables and objects happens in Queue</li>
</ul>
</li>
<li>
<h3>Queue</h3>
<ul>
<li>All the callback functions are stored here</li>
</ul>
</li>
<li>
<h3>Event Loop</h3>
<ul>
<li>Continuously monitors Call stack and Queue,</li>
<li>
If call stack becomes empty, it push the callback fn from Queue to
call stack
</li>
</ul>
</li>
</ul>
<h2 class="mume-header" id="2-data-types">2. Data Types</h2>
<ul>
<li>
<h3>Primitive types</h3>
<p>Stored in Stack memory, has fast access time & less storage</p>
<ul>
<li>string : <code>"hello"</code></li>
<li>number : <code>12, 3.1415</code></li>
<li>boolean : <code>true, false</code></li>
<li>undefined</li>
<li>null</li>
</ul>
</li>
<li>
<h3>Reference/Non primitive types</h3>
<p>Stored in Heap memory, has low access time but more storage</p>
<ul>
<li>
Objects :
<code>const person = { name: "vikas", age: 22 } ;</code>
<ul>
<li>Array : <code>let arr = [1, 2, 3, 4] ;</code></li>
</ul>
</li>
</ul>
</li>
<li>
<h3>Variables</h3>
<ul>
<li>
<p>
<strong>let</strong> : scope within current execution context
i.e block and sub block have different scope
</p>
<pre
data-role="codeBlock"
data-info="js"
class="language-javascript"><span class="token keyword keyword-let">let</span> x <span class="token operator">=</span> <span class="token number">1</span><span class="token punctuation">;</span>
<span class="token keyword control-flow keyword-if">if</span> <span class="token punctuation">(</span>x <span class="token operator">===</span> <span class="token number">1</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword keyword-let">let</span> x <span class="token operator">=</span> <span class="token number">2</span><span class="token punctuation">;</span>
<span class="token console class-name">console</span><span class="token punctuation">.</span><span class="token method function property-access">log</span><span class="token punctuation">(</span>x<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 2</span>
<span class="token punctuation">}</span>
<span class="token console class-name">console</span><span class="token punctuation">.</span><span class="token method function property-access">log</span><span class="token punctuation">(</span>x<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 1</span>
</pre>
</li>
<li>
<p>
<strong>var</strong> : scope within the function i.e, within
entire enclosing function
</p>
<pre
data-role="codeBlock"
data-info="js"
class="language-javascript"><span class="token keyword keyword-var">var</span> x <span class="token operator">=</span> <span class="token number">1</span><span class="token punctuation">;</span>
<span class="token keyword keyword-function">function</span> <span class="token function">foo</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword keyword-var">var</span> y <span class="token operator">=</span> <span class="token number">2</span><span class="token punctuation">;</span>
<span class="token console class-name">console</span><span class="token punctuation">.</span><span class="token method function property-access">log</span><span class="token punctuation">(</span>x<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 1 (function `foo` closes over `x`)</span>
<span class="token console class-name">console</span><span class="token punctuation">.</span><span class="token method function property-access">log</span><span class="token punctuation">(</span>y<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 2 (`y` is in scope)</span>
<span class="token punctuation">}</span>
<span class="token function">foo</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token console class-name">console</span><span class="token punctuation">.</span><span class="token method function property-access">log</span><span class="token punctuation">(</span>x<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 1 (`x` is in scope)</span>
<span class="token console class-name">console</span><span class="token punctuation">.</span><span class="token method function property-access">log</span><span class="token punctuation">(</span>y<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// ReferenceError, `y` is scoped to `foo`</span>
</pre>
</li>
<li>
<p>
<strong>const</strong> : block scope, value can't be
changed once it's initiated.<br />
<code>const pi = 3.24;</code>
</p>
</li>
</ul>
</li>
</ul>
<h2 class="mume-header" id="3-value-types-and-reference-types">
3. Value Types and Reference Types
</h2>
<ul>
<li>