javascript map() function code example

Example 1: javascript map array

const myArray = ['Sam', 'Alice', 'Nick', 'Matt'];

// Appends text to each element of the array
const newArray = myArray.map(name => {
	return 'My name is ' + name; 
});
console.log(newArray); // ['My name is Sam', 'My Name is Alice', ...]

// Appends the index of each element with it's value
const anotherArray = myArray.map((value, index) => index + ": " + value);
console.log(anotherArray); // ['0: Sam', '1: Alice', '2: Nick', ...]

// Starting array is unchanged
console.log(myArray); // ['Sam', 'Alice', 'Nick', 'Matt']

Example 2: javascript map function

const posts = [
  { id: 1, title: "Sample Title 1", description: "Lorem ipsum dolor sit amet, consectetur adipiscing elit..." },
  { id: 2, title: "Sample Title 2", description: "Lorem ipsum dolor sit amet, consectetur adipiscing elit..." },
  { id: 3, title: "Sample Title 3", description: "Lorem ipsum dolor sit amet, consectetur adipiscing elit..." },
];
// ES2016+
// Create new array of post IDs. I.e. [1,2,3]
const postIds = posts.map((post) => post.id);
// Create new array of post objects. I.e. [{ id: 1, title: "Sample Title 1" }]
const postSummaries = posts.map((post) => ({ id: post.id, title: post.title }));

// ES2015
// Create new array of post IDs. I.e. [1,2,3]
var postIds = posts.map(function (post) { return post.id; });
// Create new array of post objects. I.e. [{ id: 1, title: "Sample Title 1" }]
var postSummaries = posts.map(function (post) { return { id: post.id, title: post.title }; });

Example 3: how the map function works javascript

const array = [2, 5, 9];
let squares = array.map((num) => num * num);

console.log(array); // [2, 5, 9]
console.log(squares); // [4, 25, 81]

Example 4: map javascript

function each(collection, action) {
  if (Array.isArray(collection)) {
    for (var i = 0; i < collection.length; i++) {
      action(collection[i], i, collection);
    }
  } else {
    for (var key in collection) {
      action(collection[key], key, collection);
    }
  }
}

Example 5: map javascript

function map(collection, action) {
  let result = [];
  if (Array.isArray(collection)) {
    for (let i = 0; i < collection.length; i++) {
      result.push(action(collection[i], i, collection));
    }
  }
  else {
    for (let key in collection) {
      result.push(action(collection[key], key, collection));
    }
  } return result;
}