JS: Array.prototype.splice

splice is the general way to add or remove elements of a array, at any index position.

arrayX.splice(start)

Delete all tail elements starting at index start, including it.

Return a Array of removed elements, or empty array if none removed.

// clear all elements
const xx = [3, 4, 5];
xx.splice(0);
console.log(xx.length === 0);

// remove rest starting at index 2
const xx = [0, 1, 2, 3, 4, 5];
const yy = xx.splice(2);

// array is modified
console.log(JSON.stringify(xx) === "[0,1]");

// removed items
console.log(JSON.stringify(yy) === "[2,3,4,5]");

arrayX.splice(start, n)

Delete n items.

const xx = [0, 1, 2, 3, 4, 5];

// remove 3 elements, starting at index 2
const yy = xx.splice(2, 3);

// the new value
console.log(JSON.stringify(xx) === "[0,1,5]");

// removed items
console.log(JSON.stringify(yy) === "[2,3,4]");

arrayX.splice(start, n, new1, new2, etc)

Add new items.

// example of adding element to array

const xx = [0, 1, 2, 3, 4, 5];

// add "b" before index 2
const yy = xx.splice(2, 0, "b");

console.log(JSON.stringify(xx) === `[0,1,"b",2,3,4,5]`);

// removed items
console.log(JSON.stringify(yy) === "[]");

const xx = [0, 1, 2, 3];

// insert a array as item
xx.splice(2, 0, [88, 99]);

console.log(JSON.stringify(xx) === "[0,1,[88,99],2,3]");

💡 TIP: use Spread Operator to avoid nested array.

const xx = [0, 1, 2, 3];

// a function that returns array
const ff = () => [8, 9];

// insert a array as items
xx.splice(2, 0, ...ff());

console.log(JSON.stringify(xx) === "[0,1,8,9,2,3]");

const xx = [0, 1, 2, 3, 4, 5];

/*
example of array splice, remove some, add some
start at index 2, removed 3 items, add "a"
*/
const yy = xx.splice(2, 3, "a");

// the new value
console.log( JSON.stringify( xx ) === `[0,1,"a",5]` );

// removed items
console.log( JSON.stringify( yy ) === "[2,3,4]");