freeCodeCamp/curriculum/challenges/english/10-coding-interview-prep/data-structures/create-a-map-data-structure.md

id	title	challengeType	forumTopicId
8d5823c8c441eddfaeb5bdef	Create a Map Data Structure	1	301629

Description

The next few challenges will cover maps and hash tables. Maps are data structures that store key-value pairs. In JavaScript, these are available to us as objects. Maps provide rapid lookup of stored items based on key values and are very common and useful data structures.

Instructions

Let's get some practice creating our own map. Because JavaScript objects provide a much more efficient map structure than anything we could write here, this is intended primarily as a learning exercise. However, JavaScript objects only provide us with certain operations. What if we wanted to define custom operations? Use the Map object provided here as a wrapper around a JavaScript object. Create the following methods and operations on the Map object:

• add accepts a key, value pair to add to the map.
• remove accepts a key and removes the associated key, value pair
• get accepts a key and returns the stored value
• has accepts a key and returns true if the key exists or false if it doesn't.
• values returns an array of all the values in the map
• size returns the number of items in the map
• clear empties the map

Tests

tests:
  - text: The Map data structure should exist.
    testString: assert((function() { var test = false; if (typeof Map !== 'undefined') { test = new Map() }; return (typeof test == 'object')})());
  - text: 'The Map object should have the following methods: add, remove, get, has, values, clear, and size.'
    testString: "assert((function() { var test = false; if (typeof Map !== 'undefined') { test = new Map() }; return (typeof test.add == 'function' && typeof test.remove == 'function' && typeof test.get == 'function' && typeof test.has == 'function' && typeof test.values == 'function' && typeof test.clear == 'function' && typeof test.size == 'function')})());"
  - text: The add method should add items to the map.
    testString: assert((function() { var test = false; if (typeof Map !== 'undefined') { test = new Map() }; test.add(5,6); test.add(2,3); test.add(2,5); return (test.size() == 2)})());
  - text: The has method should return true for added items and false for absent items.
    testString: assert((function() { var test = false; if (typeof Map !== 'undefined') { test = new Map() }; test.add('test','value'); return (test.has('test') && !test.has('false'))})());
  - text: The get method should accept keys as input and should return the associated values.
    testString: assert((function() { var test = false; if (typeof Map !== 'undefined') { test = new Map() }; test.add('abc','def'); return (test.get('abc') == 'def')})());
  - text: The values method should return all the values stored in the map as strings in an array.
    testString: assert((function() { var test = false; if (typeof Map !== 'undefined') { test = new Map() }; test.add('a','b'); test.add('c','d'); test.add('e','f'); var vals = test.values(); return (vals.indexOf('b') != -1 && vals.indexOf('d') != -1 && vals.indexOf('f') != -1)})());
  - text: The clear method should empty the map and the size method should return the number of items present in the map.
    testString: assert((function() { var test = false; if (typeof Map !== 'undefined') { test = new Map() }; test.add('b','b'); test.add('c','d'); test.remove('asdfas'); var init = test.size(); test.clear(); return (init == 2 && test.size() == 0)})());

Challenge Seed

var Map = function() {
  this.collection = {};
  // Only change code below this line
  
  // Only change code above this line
};

Solution

var Map = function() {
    this.collection = {};
    // Only change code below this line

    this.add = function(key,value) {
      this.collection[key] = value;
    }

    this.remove = function(key) {
      delete this.collection[key];
    }

    this.get = function(key) {
      return this.collection[key];
    }

    this.has = function(key) {
      return this.collection.hasOwnProperty(key)
    }

    this.values = function() {
      return Object.values(this.collection);
    }

    this.size = function() {
      return Object.keys(this.collection).length;
    }

    this.clear = function() {
      for(let item of Object.keys(this.collection)) {
        delete this.collection[item];
      }
    }
    // Only change code above this line
};