`Array.prototype.entries()`

Returns a new array iterator that yields [index, value] pairs.

Since ES2015 Spec ↗

Syntax

arr.entries()

Array Iterator — An iterator yielding [index, value] pairs.

for (const [i, v] of ['a', 'b'].entries()) console.log(i, v);

Output

0 a
1 b

console.log([...['x'].entries()]);

Output

[ [ 0, 'x' ] ]

Handy with destructuring in `for...of` loops when you need both the index and the value. Includes empty slots in sparse arrays as undefined.