JS: Array (overview)

Array syntax

• JS: Array (basics)

Array is object type with special purpose

JavaScript array is a Object, with a magic property key "length", and special treatement of non-negative integer string property keys "0", "1", "2", etc.

console.assert(typeof [3, 4] === "object");

because array is a Object type, we can add any property to it.

const xx = [3, 4];
xx.dog = 7;
console.log(xx);
// [ 3, 4, dog: 7 ]

const xx = [3, 4];
// array is a object, you can add properties to it
xx.dog = 7;
console.assert(Object.hasOwn(xx, "dog"));
console.assert(xx.dog === 7);

Array also has the attribute “extensible”, just like other objects. [see Prevent Adding Property]

console.assert(Reflect.isExtensible([3, 4]));

Index vs property key

The index of array is the same as string property key.

console.assert(Object.hasOwn([3, 4], "0"));

Value of non-existent index

// accessing array with non-existent index results undefined
const xx = [3];
console.assert(xx[200] === undefined);

Check if a object is true array

• JS: Array.isArray

Magic property: length

• JS: Array Length Property

Array methods

• JS: Array.prototype

String to Array

• JS: String.prototype.split

Array is iterable

That means, you can use for-of Loop and Spread Operator on them.

Array max number of elements

• JS: Array max number of elements