javascript闭包在for循环 [英] javascript closure in a for loop

问题描述

可能重复：

Javascript闭合内循环 - 简单实用示例

Javascript：闭合循环？

结果为1,2,3而不是3,3,3。如何设置上下文/范围，使作业使用正确的作用域i？

so I would like the results to be 1,2,3 instead of 3,3,3. How do I set the context/scope so that the jobs are using the correctly scoped "i"?

function buildJobs(list) {
  var jobs = [];
  for (var i = 0; i < list.length; i++) {
    var item = list[i];
    jobs.push( function() {alert(item)} );
  }
  return jobs;
}

function testJobs() {
  var jobs = buildJobs([1,2,3]);
  for (var j = 0; j < jobs.length; j++) {
    jobs[j]();
  }
}

推荐答案

内部函数与另一个立即执行的函数并接收 i 作为参数：

Wrap the inner function with a another function that's immediately executed and receives i as an argument:

function buildJobs(list) {
  var jobs = [];
  for (var i = 0; i < list.length; i++) {
    var item = list[i];
    (function(i) {
      jobs.push( function() {alert(list[i])} );
    })(i);
  }
  return jobs;
}

您现在关闭 i 是对包装函数的本地化，这是每次迭代中不同的变量。 （在原始配置中，每个内部函数都在相同的变量（在执行任何函数时其值为 3 ）。 ）

You're now closing over the i that is local to the wrapper function, which is a different variable in each iteration. (In your original configuration each inner function was closing over the same variable (whose value was 3 by the time any of the functions ever executed).)

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