Require Guarding for-in (guard-for-in)

需要约束 for-in (guard-for-in)

Looping over objects with a for in loop will include properties that are inherited through the prototype chain. This behavior can lead to unexpected items in your for loop.

在使用 for in 遍历对象时，会把从原型链继承来的属性也包括进来。这样会导致意想不到的项出现。

for (key in foo) {
    doSomething(key);
}

Note that simply checking foo.hasOwnProperty(key) is likely to cause an error in some cases; see no-prototype-builtins.

注意，在某些情况下，对 foo.hasOwnProperty(key) 做简单的检测可能会导致错误出现；查看no-prototype-builtins。

Rule Details

This rule is aimed at preventing unexpected behavior that could arise from using a for in loop without filtering the results in the loop. As such, it will warn when for in loops do not filter their results with an if statement.

此规则目的在于，阻止在 for in 遍历过程中，由于不对结果进行筛选而导致意想不到的行为发生。因此，当 for in 循环没有使用 if 语句对结果进行筛选时，该规则将会发出警告。

Examples of incorrect code for this rule:

错误 代码示例：

/*eslint guard-for-in: "error"*/

for (key in foo) {
    doSomething(key);
}

Examples of correct code for this rule:

正确 代码示例：

/*eslint guard-for-in: "error"*/

for (key in foo) {
    if (Object.prototype.hasOwnProperty.call(foo, key)) {
        doSomething(key);
    }
}

for (key in foo) {
    if ({}.hasOwnProperty.call(foo, key)) {
        doSomething(key);
    }
}

Further Reading

Version

This rule was introduced in ESLint 0.0.6.

该规则在 ESLint 0.0.6 中被引入。

Resources