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

---
id: 8d5823c8c441eddfaeb5bdef
title: Create a Map Data Structure
challengeType: 1
forumTopicId: 301629
dashedName: create-a-map-data-structure
---

# --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:

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

# --hints--

The Map data structure should exist.

```js
assert(
  (function () {
    var test = false;
    if (typeof Map !== 'undefined') {
      test = new Map();
    }
    return typeof test == 'object';
  })()
);
```

The Map object should have the following methods: add, remove, get, has, values, clear, and size.

```js
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'
    );
  })()
);
```

The add method should add items to the map.

```js
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;
  })()
);
```

The has method should return true for added items and false for absent items.

```js
assert(
  (function () {
    var test = false;
    if (typeof Map !== 'undefined') {
      test = new Map();
    }
    test.add('test', 'value');
    return test.has('test') && !test.has('false');
  })()
);
```

The get method should accept keys as input and should return the associated values.

```js
assert(
  (function () {
    var test = false;
    if (typeof Map !== 'undefined') {
      test = new Map();
    }
    test.add('abc', 'def');
    return test.get('abc') == 'def';
  })()
);
```

The values method should return all the values stored in the map as strings in an array.

```js
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
    );
  })()
);
```

The clear method should empty the map and the size method should return the number of items present in the map.

```js
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;
  })()
);
```

# --seed--

## --seed-contents--

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

# --solutions--

```js
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
};
```