Short JavaScript Array methods cheatsheet, that helps you to learn, remind, or prepare to JS interview.
- length
- concat
- join
- slice
- indexOf
- lastIndexOf
- map
- sort
- reverse
- forEach
- every
- some
- filter
- shift
- unshift
- pop
- push
- splice
['a', 'b', 'c'].length // 3
['a', 'b', 'c'].concat(['d', 'e']) // ['a', 'b', 'c', 'd', 'e']
['a', 'b', 'c'].join('_') // 'a_b_c'
['a', 'b', 'c'].slice(2) // ['c']
['a', 'b', 'c', 'b', 'b'].indexOf('b') // 1
['a', 'b', 'c', 'b', 'b'].lastIndexOf('b') // 4
[1, 2, 3, 4].map(item => item * 10) // [10, 20, 30, 40]
[1, 2, 3, 4].reduce((sum, cur) => sum + cur) // 10
[4, 2, 5, 1, 3].sort() // [1, 2, 3, 4, 5]
['a', 'b', 'c'].reverse() // ['c', 'b', 'a']
[1, 2, 3, 4].forEach(item => console.log(item))
[1, 2, 3, 4].every(item => item > 0) // true
[-1, -2, -3, 4].some(item => item > 0) // true
[1, -1, 2, -2, 3].filter(item => item > 0) // [1, 2, 3]
[1, 2, 3].shift() // 1; and base array = [2, 3]
[1, 2, 3].unshift(4, 5) // [4, 5, 1, 2, 3]
[1, 2, 3].pop() // 3; base array - [1, 2]
[1, 2, 3].push(4, 5) // 5; base array - [1, 2, 3, 4, 5]
["I'm", "learning", "JavaScript"].splice(1, 1) // ["learning"]; ["I'm", "JavaScript"]
length
Return total count of elements in array
['a', 'b', 'c'].length // 3
concat
This method merges your base array and array from arguments. Concat doesn't change the existing base array, just return new
one.
['a', 'b', 'c'].concat(['d', 'e']) // ['a', 'b', 'c', 'd', 'e']
// or you can merge arrays without any method (by spread operator)
const arr1 = ['a', 'b', 'c']
const arr2 = ['d', 'e']
const result = [...arr1, ...arr2] // ['a', 'b', 'c', 'd', 'e']
join
Return string of array elements, that separated by separator string from arguments
['a', 'b', 'c'].join('_') // 'a_b_c'
slice
Return copy of array from start and end from arguments
['a', 'b', 'c'].slice(2) // ['c']
['a', 'b', 'c'].slice(0, 1) // ['a']
indexOf
Returns index of the first founded element
['a', 'b', 'c', 'b', 'b'].indexOf('b') // 1
['a', 'b', 'c'].indexOf('d') // -1
lastIndexOf
Returns index of last founded element
['a', 'b', 'c', 'b', 'b'].lastIndexOf('b') // 4
map
Method creates a new array populated with the results of calling a provided callback
[1, 2, 3, 4].map(item => item * 10) // [10, 20, 30, 40]
reduce
The method executes a callback (from args) on each element of the array, resulting in a single output value.
[1, 2, 3, 4].reduce((sum, cur) => sum + cur) // 10
sort
Returns sorted array
[4, 2, 5, 1, 3].sort() // [1, 2, 3, 4, 5]
[4, 2, 5, 1, 3].sort((a, b) => b - a) // [5, 4, 3, 2, 1]
reverse
Method reverses an array
['a', 'b', 'c'].reverse() // ['c', 'b', 'a']
forEach
The method executes a provided function once for each array element.
[1, 2, 3, 4].forEach(item => console.log(item))
every
Returns true if callback returns true for each array element.
[1, 2, 3, 4].every(item => item > 0) // true
some
Returns true if callback returns true for any array element.
[-1, -2, -3, 4].some(item => item > 0) // true
filter
The method creates a new array with all elements that pass the test implemented by the provided callback.
[1, -1, 2, -2, 3].filter(item => item > 0) // [1, 2, 3]
shift
Removes the first element from an array
[1, 2, 3].shift() // 1; and base array = [2, 3]
unshift
Add the element to the beginning of an array
[1, 2, 3].unshift(4, 5) // 5; array - [4, 5, 1, 2, 3]
pop
Removes the last element from an array and returns that element.
[1, 2, 3].pop() // 3; base array - [1, 2]
push
The method adds one or more elements to the end of an array
[1, 2, 3].push(4, 5) // 5; base array - [1, 2, 3, 4, 5]
splice
The method changes the contents of an array by removing or replacing existing elements and/or adding new elements in place.
let arr = ["I'm", "learning", "JavaScript"];
arr.splice(1, 1); // from index 1, delete 1 element
console.log( arr ); // ["I'm", "JavaScript"]
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Top comments (6)
Wow! great source mate!
Thanks a lot!
Very easy to read and remembering the list of important JS methods.
Congrats on achieving this and thanks for sharing. :)
Thank you, Anna!
Nice! But .find(), .findIndex() is missing
wow very good