array-cheat-sheet.md

Cheat sheet: JavaScript Array methods

Finding Array elements:

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

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, '▲')  ⟼ '▲●■'

Adding or removing an element from Array:

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

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

// Middle
arr=['▲','■','●']; arr.splice(1, 1); arr ⟼ ['▲', '●']

Modifying an Array (the input Array is modified and returned):

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

Deriving a new Array from an existing Array:

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

Creating an array of length N:

[...Array(4).keys()] ⟼ [0, 1, 2, 3]