JavaScript: Array Constructor

new Array(args)

Same as without new.

Array()

Return a empty array.

Array(int_n)

int_n is integer. Return a Sparse Array with length int_n.

If int_n is negative, RangeError.

Use together with Array.prototype.fill to fill array.

WARNING: Array(3) does not actually create any element in the array at all.

// new Array(int) does not create any elements, only sets length
const xx = new Array(2);
console.log(Object.getOwnPropertyNames(xx)); // [ 'length' ]

// compare to,
const yy = [undefined, undefined];
console.log(Object.getOwnPropertyNames(yy)); // [ "0", "1", "length" ]

If you create a array by Array(4), then use the array method map to fill in, it doesn't work.

// creating array by map this way doesn't work

const xx = new Array(3);
const yy = xx.map(() => 9);
console.log(yy);

// [ <3 empty items> ]
// expected [9, 9, 9]

console.log(yy[0] !== 9);

Array(non_int_x)

non_int_x is not a integer. Result is a array with a single element non_int_x.

const xx = Array("a");
console.log(xx);
// [ "a" ]

Array(a1, a2 etc)

array of items a1, a2, etc.

const xx = Array("a", "b");
console.log(xx);
// [ "a", "b" ]

Range Function for Creating Array

Range Function for Array 🚀