yoda
要求或禁止 "Yoda" 条件
此规则报告的一些问题可通过 --fix 命令行选项自动修复
尤达条件之所以如此命名，是因为条件的字面值排在第一位，而变量排在第二位。例如，以下是 Yoda 条件：
¥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:
if ("red" === color) {
// ...
}
这被称为尤达条件，因为它读作 “如果红色等于颜色”，类似于星球大战角色尤达说话的方式。与排列操作数的其他方式比较：
¥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:
if (color === "red") {
// ...
}
这通常读作 “如果颜色等于红色”，这可以说是描述比较的更自然的方式。
¥This typically reads, “if the color equals red”, which is arguably a more natural way to describe the comparison.
Yoda 条件的支持者强调不可能错误地使用 = 而不是 ==，因为你不能分配给字面值。这样做会导致语法错误，并且你会在早期被告知错误。因此，这种做法在工具尚不可用的早期编程中非常普遍。
¥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 条件的反对者指出，工具使我们成为更好的程序员，因为工具会发现错误使用 = 而不是 ==（ESLint 会为你发现这一点）。因此，他们认为，该模式的实用性并没有超过使用 Yoda 条件时代码对可读性的影响。
¥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.
规则详情
¥Rule Details
此规则旨在强制执行一致的条件样式，将变量与字面值进行比较。
¥This rule aims to enforce consistent style of conditions which compare a variable to a literal value.
选项
¥Options
此规则可以采用字符串选项：
¥This rule can take a string option:
-
如果是默认的
"never"，那么比较绝对不能是 Yoda 条件。¥If it is the default
"never", then comparisons must never be Yoda conditions. -
如果是
"always"，那么字面量值必须始终排在第一位。¥If it is
"always", then the literal value must always come first.
默认的 "never" 选项可以在对象字面量中包含异常选项：
¥The default "never" option can have exception options in an object literal:
-
如果
"exceptRange"属性是true，则规则允许范围比较中的 Yoda 条件直接括在括号中，包括if或while条件的括号。默认值为false。范围比较测试变量是否在两个字面值之间的范围之内或之外。¥If the
"exceptRange"property istrue, the rule allows Yoda conditions in range comparisons which are wrapped directly in parentheses, including the parentheses of aniforwhilecondition. The default value isfalse. A range comparison tests whether a variable is inside or outside the range between two literal values. -
如果
"onlyEquality"属性是true，则规则仅报告相等运算符==和===的 Yoda 条件。默认值为false。¥If the
"onlyEquality"property istrue, the rule reports Yoda conditions only for the equality operators==and===. The default value isfalse.
onlyEquality 选项允许 exceptRange 允许的异常的超集，因此这两个选项不能一起使用。
¥The onlyEquality option allows a superset of the exceptions which exceptRange allows, thus both options are not useful together.
never
默认 "never" 选项的错误代码示例：
¥Examples of incorrect code for the default "never" option:
/*eslint yoda: "error"*/
if ("red" === color) {
// ...
}
if (`red` === color) {
// ...
}
if (`red` === `${color}`) {
// ...
}
if (true == flag) {
// ...
}
if (5 > count) {
// ...
}
if (-1 < str.indexOf(substr)) {
// ...
}
if (0 <= x && x < 1) {
// ...
}
默认 "never" 选项的正确代码示例：
¥Examples of correct code for the default "never" option:
/*eslint yoda: "error"*/
if (5 & value) {
// ...
}
if (value === "red") {
// ...
}
if (value === `red`) {
// ...
}
if (`${value}` === `red`) {
}
exceptRange
"never", { "exceptRange": true } 选项的正确代码示例：
¥Examples of correct code for the "never", { "exceptRange": true } options:
/*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)) {
// ...
}
if (`blue` < x && x < `green`) {
// ...
}
function howLong(arr) {
return (0 <= arr.length && arr.length < 10) ? "short" : "long";
}
onlyEquality
"never", { "onlyEquality": true } 选项的正确代码示例：
¥Examples of correct code for the "never", { "onlyEquality": true } options:
/*eslint yoda: ["error", "never", { "onlyEquality": true }]*/
if (x < -1 || 9 < x) {
}
if (x !== 'foo' && 'bar' != x) {
}
if (x !== `foo` && `bar` != x) {
}
always
"always" 选项的错误代码示例：
¥Examples of incorrect code for the "always" option:
/*eslint yoda: ["error", "always"]*/
if (color == "blue") {
// ...
}
if (color == `blue`) {
// ...
}
"always" 选项的正确代码示例：
¥Examples of correct code for the "always" option:
/*eslint yoda: ["error", "always"]*/
if ("blue" == value) {
// ...
}
if (`blue` == value) {
// ...
}
if (`blue` == `${value}`) {
// ...
}
if (-1 < str.indexOf(substr)) {
// ...
}
版本
此规则是在 ESLint v0.7.1 中引入。