Array Methods

Question 1

arr.push

Answer 1

Adds items to the end
arr.push(…items)

Question 2

arr.pop()

Answer 2

Take away an item from the end

Question 3

arr.shift()

Answer 3

takes away item from the beginning

Question 4

arr.unshift()

Answer 4

adds item to the beginning
arr.unshift(…items)

Question 5

splice()

Answer 5

swiss army knives of arrays- can insert, remove, and replace elements
arr.splice(start, delete, replace/insert)
returns array of removed elements
ex: let arr = [“I”, “study”, “JavaScript”, “right”, “now”];

// remove 2 first elements
let removed = arr.splice(0, 2);

alert( removed ); // “I”, “study” <– array of removed elements

let arr = [“I”, “study”, “JavaScript”];

// from index 2
// delete 0
// then insert “complex” and “language”
arr.splice(2, 0, “complex”, “language”);

alert( arr ); // “I”, “study”, “complex”, “language”, “JavaScript”

Negative indexes: specify position from end of array

Question 6

arr.slice()

Answer 6

returns new array copying all items passed as parameters
arr.slice(start, end)
arr.slice() by itself creates a copy– used to make a copy and make changes

Question 7

arr.concat()

Answer 7

creates a new array that includes values from other arrays and additional items
arr.concat(arg1, arg2…)
takes arrays and values as arguments
can’t pass objects unless use: Symbol.isConcatSpreadable property -> treated like an array

Question 8

Symbol.isConcatSpreadable

Answer 8

Used so objects can be concatenated

let arr = [1, 2];

let arrayLike = {
0: “something”,
1: “else”,
[Symbol.isConcatSpreadable]: true,
length: 2
};

alert( arr.concat(arrayLike) ); // 1,2,something,else