如何避免 JavaScript 循環中的閉包問題？

JavaScript Closure Inside Loops: A Practical Example

The issue encountered when iterating through loops and storing anonymous functions is that the variables within these functions reference the same variable outside the loop. This can lead to unexpected behavior when trying to log the values of these variables.

Solution 1: ES6 Let Statement

ES6 introduces the let keyword, which creates a new variable scope for each iteration of the loop. This ensures that each anonymous function has its own distinct variable, resolving the closure issue.

<code class="js">for (let i = 0; i < 3; i++) {
  funcs[i] = function() {
    console.log("My value:", i);
  };
}</code>

Solution 2: ES5.1 ForEach Method

For situations primarily involving array iteration, the forEach method provides a straightforward solution. Each iteration of the callback function will have its own closure and will receive the current element of the array.

<code class="js">var someArray = [...];
someArray.forEach(function(arrayElement) {
  // Code for the specific array element
  // ...
});</code>

Solution 3: Classic Closure

Another solution is to bind the variable within each function to a separate, unchanging value outside the function. This can be achieved using a helper function:

<code class="js">function createFunc(i) {
  return function() {
    console.log("My value:", i);
  };
}

for (var i = 0; i < 3; i++) {
  funcs[i] = createFunc(i);
}</code>

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