one-var

强制变量在函数中一起或单独声明

一些该规则报告的问题可以通过 --fix 命令行选项自动修复

可以使用 var、let 或 const 在 JavaScript 代码中的任何位置声明变量。有许多与变量声明相关的样式和偏好，其中之一就是决定在单个函数中应该允许多少个变量声明。

在这方面有两种思想流派：

函数中的所有变量都应该只有一个变量声明。该声明通常出现在函数的顶部。
您应该为要定义的每个变量使用一个变量声明。

例如：

// one variable declaration per function
function foo() {
    var bar, baz;
}

// multiple variable declarations per function
function foo() {
    var bar;
    var baz;
}

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规则详情

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选项

i/QWu02im19/lo5J+rk5/bqKbtYRc/gUWXDy5VMj1O2Q4rN/XTMGxwcboa96uZhEHIeS+X1+9TAevRbtWS5Xnlgq1K5ZPtcybIRrwph64f8=

Pj+D0CO1BzCbtd4WG/uHBBdQ2g85Ey8Owh/LH8k9Mto=

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Pb5+1WOLq15kqaMvmoI3OQ==

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fZox8gSkM0cMShTJkiVdTJx/S3tGCTHKLYZJfmd6JKo=

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always

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/*eslint one-var: ["error", "always"]*/

function foo() {
    var bar;
    var baz;
    let qux;
    let norf;
}

function foo(){
    const bar = false;
    const baz = true;
    let qux;
    let norf;
}

function foo() {
    var bar;

    if (baz) {
        var qux = true;
    }
}

class C {
    static {
        var foo;
        var bar;
    }

    static {
        var foo;
        if (bar) {
            var baz = true;
        }
    }

    static {
        let foo;
        let bar;
    }
}

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/*eslint one-var: ["error", "always"]*/

function foo() {
    var bar,
        baz;
    let qux,
        norf;
}

function foo(){
    const bar = true,
        baz = false;
    let qux,
        norf;
}

function foo() {
    var bar,
        qux;

    if (baz) {
        qux = true;
    }
}

function foo(){
    let bar;

    if (baz) {
        let qux;
    }
}

class C {
    static {
        var foo, bar;
    }

    static {
        var foo, baz;
        if (bar) {
            baz = true;
        }
    }

    static {
        let foo, bar;
    }

    static {
        let foo;
        if (bar) {
            let baz;
        }
    }
}

never

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/*eslint one-var: ["error", "never"]*/

function foo() {
    var bar,
        baz;
    const bar = true,
        baz = false;
}

function foo() {
    var bar,
        qux;

    if (baz) {
        qux = true;
    }
}

function foo(){
    let bar = true,
        baz = false;
}

class C {
    static {
        var foo, bar;
        let baz, qux;
    }
}

vLn68i7rFOv8nwd/Nio849hlSHRj4wJbKa8XHVQ2BS+yCKYnZJrBOkWioZjKGPk/qyfWmMK4DyA6uOKv19yHTfWh9EOOKv0ZHij7BWjwiVM=

/*eslint one-var: ["error", "never"]*/

function foo() {
    var bar;
    var baz;
}

function foo() {
    var bar;

    if (baz) {
        var qux = true;
    }
}

function foo() {
    let bar;

    if (baz) {
        let qux = true;
    }
}

class C {
    static {
        var foo;
        var bar;
        let baz;
        let qux;
    }
}

// declarations with multiple variables are allowed in for-loop initializers
for (var i = 0, len = arr.length; i < len; i++) {
    doSomething(arr[i]);
}

consecutive

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/*eslint one-var: ["error", "consecutive"]*/

function foo() {
    var bar;
    var baz;
}

function foo(){
    var bar = 1;
    var baz = 2;

    qux();

    var qux = 3;
    var quux;
}

class C {
    static {
        var foo;
        var bar;
        let baz;
        let qux;
    }
}

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/*eslint one-var: ["error", "consecutive"]*/

function foo() {
    var bar,
        baz;
}

function foo(){
    var bar = 1,
        baz = 2;

    qux();

    var qux = 3,
        quux;
}

class C {
    static {
        var foo, bar;
        let baz, qux;
        doSomething();
        let quux;
        var quuux;
    }
}

var、let、和 const

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/*eslint one-var: ["error", { var: "always", let: "never", const: "never" }]*/
/*eslint-env es6*/

function foo() {
    var bar;
    var baz;
    let qux,
        norf;
}

function foo() {
    const bar = 1,
          baz = 2;
    let qux,
        norf;
}

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/*eslint one-var: ["error", { var: "always", let: "never", const: "never" }]*/
/*eslint-env es6*/

function foo() {
    var bar,
        baz;
    let qux;
    let norf;
}

function foo() {
    const bar = 1;
    const baz = 2;
    let qux;
    let norf;
}

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/*eslint one-var: ["error", { var: "never" }]*/
/*eslint-env es6*/

function foo() {
    var bar,
        baz;
}

vLn68i7rFOv8nwd/Nio8433g5OJmce4MUUrgcMZCTHwB+bAmGyYYtAPDbt8hv/joTPG68LhrdRLyAgeCiMOONWfnWZ5mWR8FNeZHahVsDbE=

/*eslint one-var: ["error", { var: "never" }]*/
/*eslint-env es6*/

function foo() {
    var bar,
        baz;
    const bar = 1; // `const` and `let` declarations are ignored if they are not specified
    const baz = 2;
    let qux;
    let norf;
}

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/*eslint one-var: ["error", { separateRequires: true, var: "always" }]*/
/*eslint-env node*/

var foo = require("foo"),
    bar = "bar";

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/*eslint one-var: ["error", { separateRequires: true, var: "always" }]*/
/*eslint-env node*/

var foo = require("foo");
var bar = "bar";

var foo = require("foo"),
    bar = require("bar");

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/*eslint one-var: ["error", { var: "never", let: "consecutive", const: "consecutive" }]*/
/*eslint-env es6*/

function foo() {
    let a,
        b;
    let c;

    var d,
        e;
}

function foo() {
    const a = 1,
        b = 2;
    const c = 3;

    var d,
        e;
}

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/*eslint one-var: ["error", { var: "never", let: "consecutive", const: "consecutive" }]*/
/*eslint-env es6*/

function foo() {
    let a,
        b;

    var d;
    var e;

    let f;
}

function foo() {
    const a = 1,
          b = 2;

    var c;
    var d;

    const e = 3;
}

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/*eslint one-var: ["error", { var: "consecutive" }]*/
/*eslint-env es6*/

function foo() {
    var a;
    var b;
}

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/*eslint one-var: ["error", { var: "consecutive" }]*/
/*eslint-env es6*/

function foo() {
    var a,
        b;
    const c = 1; // `const` and `let` declarations are ignored if they are not specified
    const d = 2;
    let e;
    let f;
}

initialized 和 uninitialized

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/*eslint one-var: ["error", { "initialized": "always", "uninitialized": "never" }]*/
/*eslint-env es6*/

function foo() {
    var a, b, c;
    var foo = true;
    var bar = false;
}

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/*eslint one-var: ["error", { "initialized": "always", "uninitialized": "never" }]*/

function foo() {
    var a;
    var b;
    var c;
    var foo = true,
        bar = false;
}

for (let z of foo) {
    doSomething(z);
}

let z;
for (z of foo) {
    doSomething(z);
}

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/*eslint one-var: ["error", { "initialized": "never" }]*/
/*eslint-env es6*/

function foo() {
    var foo = true,
        bar = false;
}

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/*eslint one-var: ["error", { "initialized": "never" }]*/

function foo() {
    var foo = true;
    var bar = false;
    var a, b, c; // Uninitialized variables are ignored
}

vLn68i7rFOv8nwd/Nio84xQgjhmdXsTuDCVdFnOUo3psfdLuXy94MvjTCzDOAgRajuNVjhfUoYdlUAcb5H57sRteT1ofxN9xMV94PhMdd6uN/Wn4dYu88IqKdWeA1UrvSmzfqgoXa596XiBMWGNdI7thHzPjEBr7mGqVa6Qm75g=

/*eslint one-var: ["error", { "initialized": "consecutive", "uninitialized": "never" }]*/

function foo() {
    var a = 1;
    var b = 2;
    var c,
        d;
    var e = 3;
    var f = 4;
}

vLn68i7rFOv8nwd/Nio84xQgjhmdXsTuDCVdFnOUo3psfdLuXy94MvjTCzDOAgRajuNVjhfUoYdlUAcb5H57sRteT1ofxN9xMV94PhMdd6uN/Wn4dYu88IqKdWeA1UrvuKdiKKjFp2ufj5/buzntaJpByxS9RzCc1LppB9hQ5lU=

/*eslint one-var: ["error", { "initialized": "consecutive", "uninitialized": "never" }]*/

function foo() {
    var a = 1,
        b = 2;
    var c;
    var d;
    var e = 3,
        f = 4;
}

vLn68i7rFOv8nwd/Nio84xQgjhmdXsTuDCVdFnOUo3psfdLuXy94MvjTCzDOAgRagY9cn6CIpb+jsQd2OWBS4e3136l7+DcOS5yCsfbMBVPif2c5Y/6Kxd2/MYNFcv+n

/*eslint one-var: ["error", { "initialized": "consecutive" }]*/

function foo() {
    var a = 1;
    var b = 2;

    foo();

    var c = 3;
    var d = 4;
}

vLn68i7rFOv8nwd/Nio84xQgjhmdXsTuDCVdFnOUo3psfdLuXy94MvjTCzDOAgRagY9cn6CIpb+jsQd2OWBS4aZ5bb9/mDKGioeOMsNgUEeYUjdr06Mfma84odiUCTfS

/*eslint one-var: ["error", { "initialized": "consecutive" }]*/

function foo() {
    var a = 1,
        b = 2;

    foo();

    var c = 3,
        d = 4;
}

兼容性

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