Require or disallow Yoda Conditions (yoda)

要求或者禁止Yoda条件 (yoda)

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。

Yoda conditions are so named because the literal value of the condition comes first while the variable comes second. For example, the following is a Yoda condition:

Yoda 条件被如此命名,是因为在条件判断中字面量在先而变量在第二的位置。例如,以下是 Yoda 条件:

if ("red" === color) {
    // ...
}

This is called a Yoda condition because it reads as, “if red equals the color”, similar to the way the Star Wars character Yoda speaks. Compare to the other way of arranging the operands:

它被叫做 Yoda 条件是因为它这样读:”红色是颜色”,类似于星球大战中 Yoda 的讲话方式。对比另一种操作数的排序方式:

if (color === "red") {
    // ...
}

This typically reads, “if the color equals red”, which is arguably a more natural way to describe the comparison.

这通常读作,”颜色是红的”,这是一种更自然的方式去描述对比。

Proponents of Yoda conditions highlight that it is impossible to mistakenly use = instead of == because you cannot assign to a literal value. Doing so will cause a syntax error and you will be informed of the mistake early on. This practice was therefore very common in early programming where tools were not yet available.

Yoda 条件的支持者强调,错误地使用 = 代替 == 是不可能的,因为你不能分配给一个文本值。这样做将导致一个语法错误,并且你会被提早告知。因此在工具尚不可用的早期编程中,这种做法是非常常见的。

Opponents of Yoda conditions point out that tooling has made us better programmers because tools will catch the mistaken use of = instead of == (ESLint will catch this for you). Therefore, they argue, the utility of the pattern doesn’t outweigh the readability hit the code takes while using Yoda conditions.

Yoda 条件的反对者指出工具使我们成为更好的程序员,因为工具将捕获使用 = 代替 == 的错误(ESLint 将为你捕获这个错误)。因此,他们认为当使用 Yoda 条件时,该模式的实用性并不高于代码的可读性。

Rule Details

This rule aims to enforce consistent style of conditions which compare a variable to a literal value.

这条规则需要一个参数。如果是 "never" 那么比较绝不能是一个 Yoda 条件。

Options

This rule can take a string option:

该规则只有一个字符串选项:

The default "never" option can have exception options in an object literal:

默认选项 "never" 可以有例外情况,是个对象:

The onlyEquality option allows a superset of the exceptions which exceptRange allows, thus both options are not useful together.

onlyEquality 选项所允许的是 exceptRange 所允许的例外的超集,因此同时使用它们什么用。

never

Examples of incorrect code for the default "never" option:

默认选项"never"错误 代码示例:

/*eslint yoda: "error"*/

if ("red" === color) {
    // ...
}

if (true == flag) {
    // ...
}

if (5 > count) {
    // ...
}

if (-1 < str.indexOf(substr)) {
    // ...
}

if (0 <= x && x < 1) {
    // ...
}

Examples of correct code for the default "never" option:

默认选项 "never"正确 代码示例:

/*eslint yoda: "error"*/

if (5 & value) {
    // ...
}

if (value === "red") {
    // ...
}

exceptRange

Examples of correct code for the "never", { "exceptRange": true } options:

选项 "never", { "exceptRange": true }正确 代码示例:

/*eslint yoda: ["error", "never", { "exceptRange": true }]*/

function isReddish(color) {
    return (color.hue < 60 || 300 < color.hue);
}

if (x < -1 || 1 < x) {
    // ...
}

if (count < 10 && (0 <= rand && rand < 1)) {
    // ...
}

function howLong(arr) {
    return (0 <= arr.length && arr.length < 10) ? "short" : "long";
}

onlyEquality

Examples of correct code for the "never", { "onlyEquality": true } options:

选项 "never", { "onlyEquality": true }正确 代码示例:

/*eslint yoda: ["error", "never", { "onlyEquality": true }]*/

if (x < -1 || 9 < x) {
}

if (x !== 'foo' && 'bar' != x) {
}

always

Examples of incorrect code for the "always" option:

选项 "always"错误 代码示例:

/*eslint yoda: ["error", "always"]*/

if (color == "blue") {
    // ...
}

Examples of correct code for the "always" option:

选项 "always"正确 代码示例:

/*eslint yoda: ["error", "always"]*/

if ("blue" == value) {
    // ...
}

if (-1 < str.indexOf(substr)) {
    // ...
}

Further Reading

Version

This rule was introduced in ESLint 0.7.1.

该规则在 ESLint 0.7.1 中被引入。

Resources


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