marco-ippolito/proposal-array-zip

Proposal to add Array.zip to JavaScript

Array.zip for JavaScript

Champions: Marco Ippolito

Author: Marco Ippolito

Stage: 0

This is a proposal to add the static method zip to JavaScript's built-in Array class.

Motivation

Addressing element-wise array combination in JavaScript is a common problem. The existing solutions in JavaScript lack ergonomic and performance. The absence of a dedicated Array.zip method leaves developers resorting to intricate workarounds. These workarounds are not efficient and potentially potentially error prone.

Comparison with other languages

See other languages document to get overview of Array.zip methods in other languages.

Proposal

The Array.zip method enriches the JavaScript Array class with a tool for element-wise array combination.

This would add the following method:

• Array.zip(...arrays)
• Array.zip(...arrays, mapFn)
• Array.zip(...arrays, mapFn, thisArg)

Parameters

• args - Arrays to zip.
• mapFn - Function to call on every element of the zipped arrays. It accepts the following arguments:
  • ...args - N-th elements of the zipped arrays in order.
  • index - The index of the element in the original array.
  • array - The original array.
• thisArg - Value to use as this when executing mapFn.

Examples

// zips two arrays
Array.zip(['a', 'b', 'c'], [1, 2, 3]) // [['a', 1], ['b', 2], ['c', 3]]

// zips three arrays
Array.zip(['a', 'b', 'c'], [1, 2, 3], [true, false, true]) // [['a', 1, true], ['b', 2, false], ['c', 3, true]]

If arrays have different sized, the resulting array will have the length of the shortest array:

Array.zip(['a', 'b', 'c'], [1, 2]) // [['a', 1], ['b', 2]]

Using the mapFn argument:

Array.zip(['a', 'b', 'c'], [1, 2, 3], (a, b, index, array) => ({ [a]: b })) // [{ a: 1}, {b: 2}, {c: 3}]

Using the mapFn with 3 arguments:

Array.zip(['a', 'b', 'c'], [1, 2, 3], [true, false, true], (a, b, c, index, array) => ({ [a]: c ? b : null })) // [{ a: 1}, {b: null}, {c: 3}]

Using the mapFn and thisArg arguments:

Array.zip(['a', 'b', 'c'], [1, 2, 3], (a, b, index, array)  =>  ({ [a]: b + this.offset }), { offset: 10 }) // [{ a: 11}, {b: 12}, {c: 13}]