Disallow Functions in Loops (no-loop-func)

禁止循环中存在函数 (no-loop-func)

Writing functions within loops tends to result in errors due to the way the function creates a closure around the loop. For example:

由于函数在循环中创建闭包的方式不同，在循环中编写函数往往会导致错误。例如:

for (var i = 0; i < 10; i++) {
    funcs[i] = function() {
        return i;
    };
}

In this case, you would expect each function created within the loop to return a different number. In reality, each function returns 10, because that was the last value of i in the scope.

在这个例子中，你希望在循环中创建的每个函数返回一个不同的数字。实际上，每个函数都返回作用域中 i 的最后一个值 10。

let or const mitigate this problem.

let 或 const 规避了这个问题。

/*eslint-env es6*/

for (let i = 0; i < 10; i++) {
    funcs[i] = function() {
        return i;
    };
}

In this case, each function created within the loop returns a different number as expected.

在本例中，循环中创建的每个函数都返回一个与预期不同的数字。

Rule Details

This error is raised to highlight a piece of code that may not work as you expect it to and could also indicate a misunderstanding of how the language works. Your code may run without any problems if you do not fix this error, but in some situations it could behave unexpectedly.

这个错误的出现会导致代码可能无法像你期望的那样运行，还可能表示对该语言的工作方式存在误解。 如果不修复此错误，代码可能会正常运行，但在某些情况下，可能会出现意想不到的行为。

This rule disallows any function within a loop that contains unsafe references (e.g. to modified variables from the outer scope).

此规则禁止在循环中包含不安全引用的任何函数(例如，在外部作用域中修改变量)。

Examples of incorrect code for this rule:

错误 代码示例：

/*eslint no-loop-func: "error"*/
/*eslint-env es6*/

for (var i=10; i; i--) {
    (function() { return i; })();
}

while(i) {
    var a = function() { return i; };
    a();
}

do {
    function a() { return i; };
    a();
} while (i);

let foo = 0;
for (let i = 0; i < 10; ++i) {
    //Bad, `foo` is not in the loop-block's scope and `foo` is modified in/after the loop
    setTimeout(() => console.log(foo));
    foo += 1;
}

for (let i = 0; i < 10; ++i) {
    //Bad, `foo` is not in the loop-block's scope and `foo` is modified in/after the loop
    setTimeout(() => console.log(foo));
}
foo = 100;

Examples of correct code for this rule:

正确 代码示例：

/*eslint no-loop-func: "error"*/
/*eslint-env es6*/

var a = function() {};

for (var i=10; i; i--) {
    a();
}

for (var i=10; i; i--) {
    var a = function() {}; // OK, no references to variables in the outer scopes.
    a();
}

for (let i=10; i; i--) {
    var a = function() { return i; }; // OK, all references are referring to block scoped variables in the loop.
    a();
}

var foo = 100;
for (let i=10; i; i--) {
    var a = function() { return foo; }; // OK, all references are referring to never modified variables.
    a();
}
//... no modifications of foo after this loop ...

Version

This rule was introduced in ESLint 0.0.9.

该规则在 ESLint 0.0.9 中被引入。

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