disallow constant expressions in conditions (no-constant-condition)

禁止在条件中使用常量表达式 (no-constant-condition)

The "extends": "eslint:recommended" property in a configuration file enables this rule.

配置文件中的 "extends": "eslint:recommended" 属性启用了此规则。

A constant expression (for example, a literal) as a test condition might be a typo or development trigger for a specific behavior. For example, the following code looks as if it is not ready for production.

将一个常量表达式（比如，一个字面值）作为一个测试条件可能是个书写错误或者为了触发某个特定的行为。例如，下面的代码看起来像是没有准备好发布的。

if (false) {
    doSomethingUnfinished();
}

Rule Details

This rule disallows constant expressions in the test condition of:

该规则禁止在以下语句的条件中出现常量表达式：

if, for, while, or do...while statement
if、for、while 或 do...while 语句
?: ternary expression
?: 三元表达式

Examples of incorrect code for this rule:

错误代码示例：

/*eslint no-constant-condition: "error"*/

if (false) {
    doSomethingUnfinished();
}

if (void x) {
    doSomethingUnfinished();
}

for (;-2;) {
    doSomethingForever();
}

while (typeof x) {
    doSomethingForever();
}

do {
    doSomethingForever();
} while (x = -1);

var result = 0 ? a : b;

Examples of correct code for this rule:

正确代码示例：

/*eslint no-constant-condition: "error"*/

if (x === 0) {
    doSomething();
}

for (;;) {
    doSomethingForever();
}

while (typeof x === "undefined") {
    doSomething();
}

do {
    doSomething();
} while (x);

var result = x !== 0 ? a : b;

Options

checkLoops

Set to true by default. Setting this option to false allows constant expressions in loops.

默认为 true。设置该选项为 false 允许在循环中使用常量表达式。

Examples of correct code for when checkLoops is false:

当 checkLoops 为 false 时的正确代码示例：

/*eslint no-constant-condition: ["error", { "checkLoops": false }]*/

while (true) {
    doSomething();
    if (condition()) {
        break;
    }
};

for (;true;) {
    doSomething();
    if (condition()) {
        break;
    }
};

do {
    doSomething();
    if (condition()) {
        break;
    }
} while (true)

Version

This rule was introduced in ESLint 0.4.1.