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      • Iterator.range S2

      Proposal details
      Proposal overview

      This proposal introduces Iterator.range to JavaScript, providing a built-in way to generate arithmetic sequences with support for increments, decrements, steps, decimal steps, BigInt, and infinite sequences. It aims to replace the numerous third-party implementations and improve developer productivity and performance.

      Note

      The README below comes from the upstream repository and may contain outdated stage or status metadata. Use the proposal details above as the current source of truth.

      Iterator.range

      Champions: Jack Works

      Author: Jack Works

      Stage: 2

      This proposal describes adding Iterator.range to JavaScript.

      See the rendered spec at here.

      Compare with other languages (Work in progress)

      Playground

      Polyfill

      Motivation

      • because we don't have it yet™

      Without these functions, the language feels incomplete, and is a paper cut to what could be a very polished experience. Bringing this into the platform will improve performance of the web, and developer productivity as they no longer have to implement these common functions.

      —— String.prototype.{padStart,padEnd}

      range is a very useful function. For example in Python:

      for i in range(5):
    # ...

      At least 20 different implementations in a single stackoverflow question.

      Tons of libraries providing a range: math.js, lodash, underscore.js, ramda, d3, range, fill-range, multi-integer-range, ……

      Goals

      • Arithmetic Sequence
        • Incremental (0, 1, 2, 3, ...)
        • Decremental (0, -1, -2, -3, ...)
        • Step (0, 2, 4, 6, ...)
          • Decimal step (0, 0.2, 0.4, ...)
      • BigInt Support
        • Same as Arithmetic Sequence
      • Infinite Sequence Iterator.range(0, Infinity) -> (0, 1, 2, 3, ...)

      Non-goals

      • New Syntax
      • String Sequence (a, b, c, d, ...)
      • Magic
        • E.g. if (x in Iterator.range(0, 10)) (Kotlin has this feature)

      Examples

      See tests to learn about more usages.

      for (const i of Iterator.range(0n, 43n)) console.log(i) // 0n to 42n

Iterator.range(0, Infinity)
    .take(1000)
    .filter((x) => !(x % 3))
    .toArray()

function* even() {
    for (const i of Iterator.range(0, Infinity)) if (i % 2 === 0) yield i
}
;[...Iterator.range(1, 100, 2)] // odd number from 1 to 99

      Presentations

      Signature

      See global.d.ts