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 ⟼ ['■','●']
