no-undef-init

不允许将变量初始化为 undefined

一些该规则报告的问题可以通过 --fix 命令行选项 自动修复

在 JavaScript 中，已声明但未初始化为任何值的变量会自动获取 undefined 的值。例如：

var foo;

console.log(foo === undefined);     // true

因此不必将变量初始化为 undefined，例如：

var foo = undefined;

避免将变量初始化为 undefined 被认为是最佳实践。

规则详情

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QnwhPm/cyTBJK+3dwgoJPe3E20un+2KP2CiFhQ+78TgFiUScrcmb3urZ1LYB2VeR

/*eslint no-undef-init: "error"*/

var foo = undefined;
let bar = undefined;

ZV3WTnsA6mjxcovKoGG8hTv7+Ha1z2USrMCyxcmIv+4859h0MFN8WvPgRtljmRMU

/*eslint no-undef-init: "error"*/

var foo;
let bar;

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FC+RSdmeooMDvAC8f0gSEddiBAaEMR2/ycXuzoNq0VRdhPVRiEJH+l9wvo26/vum

/*eslint no-undef-init: "error"*/

const foo = undefined;

let { bar = undefined } = baz;

[quux = undefined] = quuux;

(foo = undefined) => {};

class Foo {
    bar = undefined;
}

何时不使用

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QnwhPm/cyTBJK+3dwgoJPe3E20un+2KP2CiFhQ+78TgFiUScrcmb3urZ1LYB2VeR

for (i = 0; i < 10; i++) {
    var x = undefined;
    console.log(x);
    x = i;
}

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var x;

for (i = 0; i < 10; i++) {
    x = undefined;
    console.log(x);
    x = i;
}

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for (i = 0; i < 10; i++) {
    var x;
    console.log(x);
    x = i;
}

SIao51gtTtVx1l8fz5TTKlat1RmMeo6+bhWko2D/yjY=

var x;

for (i = 0; i < 10; i++) {
    console.log(x);
    x = i;
}

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/*eslint no-undef-init: "error"*/

for (i = 0; i < 10; i++) {
    var x = undefined; // eslint-disable-line no-undef-init
    console.log(x);
    x = i;
}