js 实现简单的parseInt和parseFloat

function myParseInt(str: string): number {

  let result = NaN;

  for (let i = 0; i < str.length; i++) {

    const dec: number = str.charCodeAt(i);

    if (dec < 48 || dec > 57) break;

    if(isNaN(result)) result = 0;

    const value = dec - 48;

    result = result * 10 + value;

  }

  return result;

}

function myParseFloat(str: string): number {

  let result = NaN;

  let isDecimal = false; // 小数点

  let decimalIndex = 0; // 小数点第几位

  const N = 1000;

  for (let i = 0; i < str.length; i++) {

    const dec: number = str.charCodeAt(i);

    const isPoint = dec === 46;

    if (isPoint && isDecimal) {

      // 再次遇到小数点直接返回

      break;

    } else if (isPoint) {

      isDecimal = true;

      continue;

    }

    if (dec < 48 || dec > 57) break;

    if (isNaN(result)) result = 0;

    const value = dec - 48;

    if (!isDecimal) {

      result = result * 10 + value;

    } else {

      decimalIndex++;

      result = (result * N + (value / 10 ** decimalIndex) * N) / N;

    }

  }

  return result;

}

console.log(myParseInt("12.22")); // 12

console.log(myParseFloat("0.22")); // 0.22
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js 实现简单的parseInt和parseFloat

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