Array.map() js 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: js array map

const array1 = [1, 4, 9, 16];

// pass a function to map
const map1 = array1.map(x => x * 2);

console.log(map1);
// expected output: Array [2, 8, 18, 32]

Example 3: functions in map javascript

const map = new Map();

function foo() {
 return "Hello World!"; 
}

map.set("foo", foo);

console.log(map.get("foo")()); // Output: "Hello World!

Example 4: 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;
}

Example 5: array mdn map

let new_array = arr.map(function callback( currentValue[, index[, array]]) {
    // return element for new_array
}[, thisArg])

Example 6: javascripr array.map

array.map( item => item.id )

array2.map( item => item.toString() )

array2.map( item => item * 3 )

// this will apply a transformation to all elements of an array
// "" item => something "" is the transformation (function)