---
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:
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
# --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
};
```