Create an Array of Given Size in JavaScript
The basic method to create an array is by using the Array constructor. We can initialize an array of certain length just by passing a single integer argument to the JavaScript array constructor. This will create an array of the given size with undefined values.
Syntax
cosnt arr = new Array( length );// Initialize an array using the array constructor
let arr = new Array(5);
// Display the length and generated array
console.log("Length of the Array:", arr.length);
console.log("Array Values: ", arr);
Output
Length of the Array: 5 Array Values: [ <5 empty items> ]
1. Using apply() and map() Methods
The apply() method is used to bind and invoke a function and the array map() method is used to transform and return a new array.
Syntax
function.apply(this, argsArray)
arr.map( ( element, index, array) => { //...code to be exected }
// Initialize an array using the apply function
let arr = Array.apply(null, Array(5)).map( function(){});
// Display the length and generated array
console.log("Length of the Array:", arr.length);
console.log("Array Values: ", arr);
Output
Length of the Array: 5 Array Values: [ undefined, undefined, undefined, undefined, undefined ]
Example: Use the apply function with array custructor to create array of length five and array.map() to place the indecies as the array elements.
// Initialize an array using the apply function
let arr = Array.apply(null, Array(5)).map(function (y, i) { return i; });
// Display the length and generated array
console.log("Length of the Array:", arr.length);
console.log("Array Values: ", arr);
Output
Length of the Array: 5 Array Values: [ 0, 1, 2, 3, 4 ]
2. Using Array from() Method
In ES6, we got something new function called Array from() method, by which we can create an array of a given size.
// Initialize an array using the array.from() method
let arr = Array.from({length:5});
// Display the length and generated array
console.log("Length of the Array:", arr.length);
console.log("Array Values: ", arr);
Output
Length of the Array: 5 Array Values: [ undefined, undefined, undefined, undefined, undefined ]
Example 2: We will pass the elements as arguments, each character will be an array element.
// Initialize an array using the array.from() method
let arr = Array.from("12345");
// Display the length and generated array
console.log("Length of the Array:", arr.length);
console.log("Array Values: ", arr);
Output
Length of the Array: 5 Array Values: [ '1', '2', '3', '4', '5' ]
Example 3: Ceating an array from single letter repeating it using string.repeat() method for 5 times.
// Initialize an array using the array.from() method
let arr = Array.from("5".repeat(5));
// Display the length and generated array
console.log("Length of the Array:", arr.length);
console.log("Array Values: ", arr);
Output
Length of the Array: 5 Array Values: [ '5', '5', '5', '5', '5' ]
Example 4: Use the Array.from() with callback arraw function to set the index as the array elements.
// Initialize an array using the array.from() method
let arr = Array.from({ length: 5 }, (element, index) => index);
// Display the length and generated array
console.log("Length of the Array:", arr.length);
console.log("Array Values: ", arr);
Output
Length of the Array: 5 Array Values: [ 0, 1, 2, 3, 4 ]
3. Using for Loop with array.push() Method
The for loop is used to repeatedly execute the given code untill the condition turns false and, the array.push() method is used to add one or more elements at the end of an array.
// Given size
const size = 5;
// Initialize empty array
const arr = [];
// Iterate and add element in each iteration
for (let i = 0; i < size; i++) {
arr.push(i);
}
// Display output
console.log("Array length", arr.length);
console.log("Array Values: ", arr);
Output
Array length 5 Array Values: [ 0, 1, 2, 3, 4 ]
