disallow unnecessary boolean casts (no-extra-boolean-cast)

禁止不必要的布尔类型转换（no-extra-boolean-cast）

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。

The --fix option on the command line can automatically fix some of the problems reported by this rule.

命令行中的 --fix 选项可以自动修复一些该规则报告的问题。

In contexts such as an if statement’s test where the result of the expression will already be coerced to a Boolean, casting to a Boolean via double negation (!!) or a Boolean call is unnecessary. For example, these if statements are equivalent:

在上下文中比如 if 语句的测试表达式的结果已经被强制转化成了一个布尔值，再通过双重否定（!!）或 Boolean 转化是不必要的。例如，这些 if 语句是等价的：

if (!!foo) {
    // ...
}

if (Boolean(foo)) {
    // ...
}

if (foo) {
    // ...
}

Rule Details

This rule disallows unnecessary boolean casts.

该规则禁止不必要的布尔类型转换。

Examples of incorrect code for this rule:

错误 代码示例：

/*eslint no-extra-boolean-cast: "error"*/

var foo = !!!bar;

var foo = !!bar ? baz : bat;

var foo = Boolean(!!bar);

var foo = new Boolean(!!bar);

if (!!foo) {
    // ...
}

if (Boolean(foo)) {
    // ...
}

while (!!foo) {
    // ...
}

do {
    // ...
} while (Boolean(foo));

for (; !!foo; ) {
    // ...
}

Examples of correct code for this rule:

正确 代码示例：

/*eslint no-extra-boolean-cast: "error"*/

var foo = !!bar;
var foo = Boolean(bar);

function foo() {
    return !!bar;
}

var foo = bar ? !!baz : !!bat;

Version

This rule was introduced in ESLint 0.4.0.

该规则在 ESLint 0.4.0 中被引入。

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