Cache With Time Limit.js

// Write a class that allows getting and setting key-value pairs, however a time until expiration is associated with each key.

// The class has three public methods:

// set(key, value, duration): accepts an integer key, an integer value, and a duration in milliseconds. Once the duration has elapsed, the key should be inaccessible. The method should return true if the same un-expired key already exists and false otherwise. Both the value and duration should be overwritten if the key already exists.

// get(key): if an un-expired key exists, it should return the associated value. Otherwise it should return -1.

// count(): returns the count of un-expired keys.

 

// Example 1:

// Input: 
// actions = ["TimeLimitedCache", "set", "get", "count", "get"]
// values = [[], [1, 42, 100], [1], [], [1]]
// timeDelays = [0, 0, 50, 50, 150]
// Output: [null, false, 42, 1, -1]
// Explanation:
// At t=0, the cache is constructed.
// At t=0, a key-value pair (1: 42) is added with a time limit of 100ms. The value doesn't exist so false is returned.
// At t=50, key=1 is requested and the value of 42 is returned.
// At t=50, count() is called and there is one active key in the cache.
// At t=100, key=1 expires.
// At t=150, get(1) is called but -1 is returned because the cache is empty.


// CODE 

const TimeLimitedCache = function() {
    this.cache = new Map();  // Using Map so we don't need a size variable
};

TimeLimitedCache.prototype.set = function(key, value, duration) {
    let found = this.cache.has(key);
    if (found) clearTimeout(this.cache.get(key).ref);  // Cancel previous timeout
    this.cache.set(key, {
        value,  // Equivalent to `value: value`
        ref: setTimeout(() => this.cache.delete(key), duration)
    });
    return found;
};

TimeLimitedCache.prototype.get = function(key) {
    return this.cache.has(key) ? this.cache.get(key).value : -1;
};

TimeLimitedCache.prototype.count = function() {
    return this.cache.size;
};