js中怎么格式化一位数变成两位数

比如我要输出的是time=8，怎么让它 变成08呢？

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if ( num < 10) {
    return "0" + num;
}

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var time = 4;
console.log((Array(2).join(0)+time).slice(-2));

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function fix(num, length) {
  return ('' + num).length < length ? ((new Array(length + 1)).join('0') + num).slice(-length) : '' + num;
}

fix(1234, 8);
// "00001234"
fix(1234, 2);
// "1234"