no-extra-boolean-cast.md

规则名	规则类型
no-extra-boolean-cast	suggestion

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:

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

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

if (foo) {
    // ...
}

规则详解

This rule disallows unnecessary boolean casts.

此规则的 错误 代码实例：

/*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; ) {
    // ...
}

此规则的 正确 代码实例：

::: correct

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

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

function foo() {
    return !!bar;
}

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

配置项

This rule has an object option:

• "enforceForLogicalOperands" when set to true, in addition to checking default contexts, checks whether the extra boolean cast is contained within a logical expression. Default is false, meaning that this rule by default does not warn about extra booleans cast inside logical expression.

enforceForLogicalOperands

Examples of incorrect code for this rule with "enforceForLogicalOperands" option set to true:

/*eslint no-extra-boolean-cast: ["error", {"enforceForLogicalOperands": true}]*/

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

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

if ((!!foo || bar) && baz) {
    //...
}

foo && Boolean(bar) ? baz : bat

var foo = new Boolean(!!bar || baz)

Examples of correct code for this rule with "enforceForLogicalOperands" option set to true:

::: correct

/*eslint no-extra-boolean-cast: ["error", {"enforceForLogicalOperands": true}]*/

if (foo || bar) {
    //...
}

while (foo && bar) {
    //...
}

if ((foo || bar) && baz) {
    //...
}

foo && bar ? baz : bat

var foo = new Boolean(bar || baz)

var foo = !!bar || baz;