javascript - 轻松理解 JavaScript 闭包中的示例

Question

http://javascriptissexy.com/understand-javascript-closures-with-ease/ 的最后一个例子是:

function celebrityIDCreator (theCelebrities) {
    var i;
    var uniqueID = 100;
    for (i = 0; i < theCelebrities.length; i++) {
        theCelebrities[i]["id"] = function (j)  { // the j parametric variable is the i passed in on invocation of this IIFE​
            return function () {
                return uniqueID + j; // each iteration of the for loop passes the current value of i into this IIFE and it saves the correct value to the array​
            } () // BY adding () at the end of this function, we are executing it immediately and returning just the value of uniqueID + j, instead of returning a function.​
        } (i); // immediately invoke the function passing the i variable as a parameter​
    }
    return theCelebrities;
};

​var actionCelebs = [{name:"Stallone", id:0}, {name:"Cruise", id:0}, {name:"Willis", id:0}];

​var createIdForActionCelebs = celebrityIDCreator (actionCelebs);

​var stalloneID = createIdForActionCelebs[0];

console.log(stalloneID.id); // 100​

console.log(createIdForActionCelebs[1].id); // 101

我不明白为什么这里需要 IIFE​，我替换了 celebrityIDCreator 并产生了相同的结果:

var celebrityIDCreator = function(theCelebrities) {
      var i;
      var uniqueID = 100;
      for (i = 0; i < theCelebrities.length; i++) {
          theCelebrities[i]["id"] = function (j) {
            return uniqueID + j;
              // return function () {

              // } () ;
          } (i);
      }

      return theCelebrities;
};

有人可以解释一下吗？我错过了什么吗？

Answer 1

我认为这是博客上的一个错误。如果您看到 Closures Gone Awry 部分的第一个示例，id 是作为函数创建的。但是，在您所指的第二个示例中，该示例旨在解决第一个示例中的错误，id 被创建为属性。

我认为第二个例子应该是这样的，以便使其与第一个例子相似。请注意代码中的注释，靠近相关 IIFE 以及将 id 作为函数使用

function celebrityIDCreator(theCelebrities) {
  var i;
  var uniqueID = 100;
  for (i = 0; i < theCelebrities.length; i++) {
    theCelebrities[i]["id"] = function(j) { // the j parametric variable is the i passed in on invocation of this IIFE
      return function() {
        return uniqueID + j; // each iteration of the for loop passes the current value of i into this IIFE and it saves the correct value to the array
      } // NOTE. Not an IIFE
    }(i); // immediately invoke the function passing the i variable as a parameter
  }
  return theCelebrities;
};


var actionCelebs = [{
  name: "Stallone",
  id: 0
}, {
  name: "Cruise",
  id: 0
}, {
  name: "Willis",
  id: 0
}];


var createIdForActionCelebs = celebrityIDCreator(actionCelebs);


var stalloneID = createIdForActionCelebs[0];

console.log(stalloneID.id()); // 100 NOTE: Use as function

console.log(createIdForActionCelebs[1].id()); // 101 NOTE: Use as function

除此之外，我相信您不会错过任何东西。如果 id 需要是一个属性，您的代码是正确的。