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// Promise all的实现
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Promise._all = function (tasks) {
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  return new Promise((resolve, reject) => {
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    if (!tasks || !tasks.length) {
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      return []
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    }
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    // 结果数组
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    let result = [];
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    // 做数量记录
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    let count = 0;
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    for (let i = 0; i < tasks.length; i++) {
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      const element = tasks[i]; // 当前的任务
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      Promise.resolve(element).then( // 需要用Promise包裹以防止当前task并不是用Promise封装的
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        (data) => {
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          result[i] = data;
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          if (++count === tasks.length) {
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            resolve(result)
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          }
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        },
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        (err) => {
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          reject(err);
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          return;
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        })
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    }
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  })
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}
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Promise._all([
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  Promise.resolve(11211),
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  Promise.resolve(21213212312),
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  new Promise((resolve) => setTimeout(() => {
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    resolve('延时')
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  }, 1000))
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]).then((data) => {
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  console.log(data);
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})