Let’s tidy up the method of JavaScript array.

Add/Delete Array

Array.push()

Add the last element of the array.

let number_arr = [1, 2, 3, 4, 5 ];
number_arr.push(6);
console.log(number_arr); // [1, 2, 3, 4, 5, 6]

Output :

[1, 2, 3, 4, 5, 6]

Array.unshift()

Add the first element of the array.

let number_arr = [1, 2, 3, 4, 5 ];
number_arr.unshift(6);
console.log(number_arr); // [6, 1, 2, 3, 4, 5]

Output :

[6, 1, 2, 3, 4, 5]

Array.pop()

Delete the last element of the array.

let number_arr = [1, 2, 3, 4, 5 ];
let pop = number_arr.pop();
console.log(number_arr); // [1, 2, 3, 4]
console.log(pop); // 5

Output :

[1, 2, 3, 4] 5

Array.shift()

Delete the first element in the array.

let number_arr = [1, 2, 3, 4, 5 ];
let shift = number_arr.shift();
console.log(number_arr); // [2, 3, 4, 5]
console.log(shift); // One

Output :

[2, 3, 4, 5] 1

Array.slice()

The existing array remains unchanged, and returns that element.

let number_arr = [1, 2, 3, 4, 5 ];
// Syntax: Array.slice (start position, end position)
let sp = number_arr.slice(1, 3); // Return from 2nd to 3rd.
console.log(number_arr); // [1 2 3 4 5]
console.log(sp); // [2, 3]
sp = number_arr.slice(2);
console.log(sp); // [3, 4, 5]

Output :

[1, 2, 3, 4, 5] [2, 3] [3, 4, 5]

Array.splice()

Delete the array at the specified position.

let number_arr = [1, 2, 3, 4, 5 ];
// Syntax: Array.splice(start position, number to delete, add_to_item...)
let sp = number_arr.splice(1, 2); // Delete 2 from the 2nd element.
console.log(number_arr); // [1, 4, 5]
console.log(sp); // [2, 3]
let sp2 = number_arr.splice(1, 0, 7, 8, 9); // Delete 0 at the second element position and add 7,8,9.
console.log(number_arr); // [1, 7, 8, 9, 4, 5]
console.log(sp2); // undefined: 0 is deleted, so there is no value.

Output :

[1, 4, 5] [2, 3] [1, 7, 8, 9, 4, 5] []

Array.concat()

Combine the arrays.

let num1 = [1, 2, 3];
let num2 = [4,5,6];
let combine = num1.concat(num2);
console.log(combine); // [1, 2, 3, 4, 5, 6]
let num3 = [7, 8, 9];
combine = num1.concat(num2, num3);
console.log(combine); // [1, 2, 3, 4, 5, 6, 7, 8, 9]

Output :

[1, 2, 3, 4, 5, 6] [1, 2, 3, 4, 5, 6, 7, 8, 9]

Array.of()

Create a new instance array as a function argument.

let ar = Array.of(1, 2, 3)
console.log(ar); // [1, 2, 3]
let ch = Array.of("Chibi", "Champon");
console.log(ch); // ["Chibi", "Champon"]

Output :

[1, 2, 3] [“Jajang”, “Champon”]

Array iteration

Array.forEach()

Iterate through the elements of an array sequentially.

let vl = ['one','two','three' ];
vl.forEach((e) => {
    console.log(e); // print one, two, three in sequence
})

Output :

one two three

The second argument returns the index of the element.

let vl = ['one','two','three' ];
vl.forEach((e, i) => {
    console.log(e, i);
})

Output :

one 0 two 1 three 2

Array.values()

Make the elements of the array a new iterative object.

let vl = ['one','two','three' ];
let iterator = vl.values();

console.log(iterator.next().value); // one
console.log(iterator.next().value); // two
console.log(iterator.next().value); // three
console.log(iterator.next().value); // undefined

Output :

one two three undefined

let vl = ['one','two','three' ];
let iterator = vl.values();

for (let i of iterator) {
    console.log(i);
}
console.log(iterator.next().value); // undefined: None of the above are repeated.

Output :

one two three

Array.entries()

Make an element of an array into a repeatable object paired by key and value.

let vl = ['one','two','three' ];
let iterator = vl.values();
for (let i of iterator) {
    console.log(i);
}

Output :

[0, "one”] [1, "two”] [2, "three”]

Find Array

Array.some()

Returns true if any element in the array matches the conditional expression.

console.log([2, 5, 8, 1, 4].some((e) => e> 5));
console.log([2, 5, 8, 1, 4].some((e) => e> 9));

Output :

true false

Array.every()

All elements in the array must match the conditional expression to return true.

console.log([2, 5, 8, 1, 4].every((e) => e <9));
console.log([2, 5, 8, 1, 4].every((e) => e> 4));

Output :

true false

Array.find()

Returns the first element of a conditional expression in an array.

console.log([2, 5, 8, 1, 4].find((e) => e <9));
console.log([2, 5, 8, 1, 4].find((e) => e> 4));

Output :

2 5

The second value is the index of the array, the third is the current array.

console.log([2, 5, 8, 1, 4].find((e, i) => e> 3 && i <2));

Output :

5

Array.findIndex()

Returns the index of the first element in the array that meets the conditional expression.

console.log([2, 5, 8, 1, 4]