JavaScript Array methods

I found myself referring to this cheat sheet by Axel Rauschmayer so much I thought I would share it:

Cheat sheet: JavaScript Array methods

Deriving a new Array from an existing Array:

['■','●','▲'].slice(1, 3)                       ⟼ ['●','▲']
['■','●','■'].filter(x => x==='■')  ⟼ ['■','■']
['▲','●'].map(x => x+x)                         ⟼ ['▲▲','●●']
['▲','●'].flatMap(x => [x,x])               ⟼ ['▲','▲','●','●']

Computing a summary of an Array:

['■','●','▲'].some(x => x==='●')  ⟼ true
['■','●','▲'].every(x => x==='●') ⟼ false
['■','●','▲'].join('-') ⟼ '■-●-▲'
['■','●'].reduce((result,x) => result+x, '▲')      ⟼ '▲■●'
['■','●'].reduceRight((result,x) => result+x, '▲') ⟼ '▲●■'

Changing all of an Array (the input Array is modified and returned):

['■','●','▲'].fill('●') ⟼ ['●','●','●']
['■','●','▲'].reverse() ⟼ ['▲','●','■']
['■','●','■'].sort()        ⟼ ['■','■','●']

Finding Array elements:

['■','●','■'].includes('■')                     ⟼ true
['■','●','■'].indexOf('■')                      ⟼ 0
['■','●','■'].lastIndexOf('■')              ⟼ 2
['■','●','■'].find(x => x==='■')            ⟼ '■'
['■','●','■'].findIndex(x => x==='■')   ⟼ 0

Listing elements (spreading via ... is needed because the methods return iterables):

[...['■','●','▲'].keys()]    ⟼ [0,1,2]
[...['■','●','▲'].values()]  ⟼ ['■','●','▲']
[...['■','●','▲'].entries()] ⟼ [[0,'■'],[1,'●'],[2,'▲']]

Adding or removing an element at either end of an Array:

arr=['■','●'];     arr.push('▲');    arr ⟼ ['■','●','▲']
arr=['■','●','▲']; arr.pop();        arr ⟼ ['■','●']
arr=['■','●'];     arr.unshift('▲'); arr ⟼ ['▲','■','●']
arr=['▲','■','●']; arr.shift();      arr ⟼ ['■','●']

Source

• Axel Rauschmayer