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JavaScriptでrange関数を作る

Last updated at Posted at 2018-06-06

備忘録。
もっと速いのがあればご教示ください。

その1 オーソドックス

const range = size => {
  const range = Array(size);
  for (let i = 0; i < size; i++) {
    range[i] = i;
  }
  return range;
};

start, stepを実装すると

const range = (start, end, step) => {
  if (typeof end === 'undefined') {
    end = start || 0;
    start = 0;
  }
  if (!step) {
    step = end > start ? 1 : -1;
  }
  const length = Math.max(Math.ceil((end - start)/step), 0);
  const range = Array(length);
  for (let i = 0; i < length; i++, start += step) {
    range[i] = start;
  }
  return range;
};
  • underscore.jsを模倣した
  • 結局これが一番早い

その2 一行

const range = size => [...Array(size).keys()];

start, stepを実装すると

const range = (start, end, step) => [...Array(Math.max(Math.ceil((end - start)/step), 0)).keys()].map(n => n*step + start);
  • 引数を省略できない(省略したけりゃその1を使う)
  • 速そうで遅い

その3 うーん

const range = size => Array.from({length: size}, (x, i) => i);

うーーん

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