no-unused-vars

禁止未使用的变量

配置文件 中的 "extends": "eslint:recommended" 属性启用了该规则

由于重构不完整，已声明但未在代码中任何地方使用的变量很可能是错误。这样的变量会占用代码中的空间，并可能导致读者混淆。

规则详情

该规则旨在消除未使用的变量、函数和函数参数。

如果以下任何一项为真，则认为使用变量 foo：

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/*eslint no-unused-vars: "error"*/
/*global some_unused_var*/

// It checks variables you have defined as global
some_unused_var = 42;

var x;

// Write-only variables are not considered as used.
var y = 10;
y = 5;

// A read for a modification of itself is not considered as used.
var z = 0;
z = z + 1;

// By default, unused arguments cause warnings.
(function(foo) {
    return 5;
})();

// Unused recursive functions also cause warnings.
function fact(n) {
    if (n < 2) return 1;
    return n * fact(n - 1);
}

// When a function definition destructures an array, unused entries from the array also cause warnings.
function getY([x, y]) {
    return y;
}

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/*eslint no-unused-vars: "error"*/

var x = 10;
alert(x);

// foo is considered used here
myFunc(function foo() {
    // ...
}.bind(this));

(function(foo) {
    return foo;
})();

var myFunc;
myFunc = setTimeout(function() {
    // myFunc is considered used
    myFunc();
}, 50);

// Only the second argument from the destructured array is used.
function getY([, y]) {
    return y;
}

exported

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/* exported global_var */

var global_var = 42;

选项

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{
    "rules": {
        "no-unused-vars": ["error", { "vars": "all", "args": "after-used", "ignoreRestSiblings": false }]
    }
}

vars

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vars: local

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/*eslint no-unused-vars: ["error", { "vars": "local" }]*/
/*global some_unused_var */

some_unused_var = 42;

varsIgnorePattern

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/*eslint no-unused-vars: ["error", { "varsIgnorePattern": "[iI]gnored" }]*/

var firstVarIgnored = 1;
var secondVar = 2;
console.log(secondVar);

args

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args: after-used

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/*eslint no-unused-vars: ["error", { "args": "after-used" }]*/

// 2 errors, for the parameters after the last used parameter (bar)
// "baz" is defined but never used
// "qux" is defined but never used
(function(foo, bar, baz, qux) {
    return bar;
})();

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/*eslint no-unused-vars: ["error", {"args": "after-used"}]*/

(function(foo, bar, baz, qux) {
    return qux;
})();

args: all

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/*eslint no-unused-vars: ["error", { "args": "all" }]*/

// 2 errors
// "foo" is defined but never used
// "baz" is defined but never used
(function(foo, bar, baz) {
    return bar;
})();

args: none

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/*eslint no-unused-vars: ["error", { "args": "none" }]*/

(function(foo, bar, baz) {
    return bar;
})();

argsIgnorePattern

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/*eslint no-unused-vars: ["error", { "argsIgnorePattern": "^_" }]*/

function foo(x, _y) {
    return x + 1;
}
foo();

caughtErrors

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caughtErrors: none

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/*eslint no-unused-vars: ["error", { "caughtErrors": "none" }]*/

try {
    //...
} catch (err) {
    console.error("errors");
}

caughtErrors: all

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/*eslint no-unused-vars: ["error", { "caughtErrors": "all" }]*/

// 1 error
// "err" is defined but never used
try {
    //...
} catch (err) {
    console.error("errors");
}

caughtErrorsIgnorePattern

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/*eslint no-unused-vars: ["error", { "caughtErrorsIgnorePattern": "^ignore" }]*/

try {
    //...
} catch (ignoreErr) {
    console.error("errors");
}

destructuredArrayIgnorePattern

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/*eslint no-unused-vars: ["error", { "destructuredArrayIgnorePattern": "^_" }]*/

const [a, _b, c] = ["a", "b", "c"];
console.log(a+c);

const { x: [_a, foo] } = bar;
console.log(foo);

function baz([_c, x]) {
    x;
}
baz();

function test({p: [_q, r]}) {
    r;
}
test();

let _m, n;
foo.forEach(item => {
    [_m, n] = item;
    console.log(n);
});

let _o, p;
_o = 1;
[_o, p] = foo;
p;

ignoreRestSiblings

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/*eslint no-unused-vars: ["error", { "ignoreRestSiblings": true }]*/
// 'foo' and 'bar' were ignored because they have a rest property sibling.
var { foo, ...coords } = data;

var bar;
({ bar, ...coords } = data);

何时不使用

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