no-unreachable
禁止在 return、throw、continue 和 break 语句后出现无法访问的代码
在 配置文件 中使用来自 @eslint/js 的 recommended 配置可以启用此规则
因为 return、throw、continue 和 break 语句无条件退出代码块，所以后面的任何语句都无法执行。无法访问的语句通常是一个错误。
¥Because the return, throw, continue, and break statements unconditionally exit a block of code, any statements after them cannot be executed. Unreachable statements are usually a mistake.
function fn() {
x = 1;
return x;
x = 3; // this will never execute
}
另一种错误是在其构造函数没有调用 super() 的子类中定义实例字段。子类的实例字段只添加到 super() 之后的实例中。如果没有 super() 调用，则它们的定义永远不会应用，因此是无法访问的代码。
¥Another kind of mistake is defining instance fields in a subclass whose constructor doesn’t call super(). Instance fields of a subclass are only added to the instance after super(). If there are no super() calls, their definitions are never applied and therefore are unreachable code.
class C extends B {
#x; // this will never be added to instances
constructor() {
return {};
}
}
规则详情
¥Rule Details
此规则不允许在 return、throw、continue 和 break 语句之后出现无法访问的代码。此规则还标记其构造函数没有 super() 调用的子类中的实例字段定义。
¥This rule disallows unreachable code after return, throw, continue, and break statements. This rule also flags definitions of instance fields in subclasses whose constructors don’t have super() calls.
此规则的错误代码示例：
¥Examples of incorrect code for this rule:
/*eslint no-unreachable: "error"*/
function foo() {
return true;
console.log("done");
}
function bar() {
throw new Error("Oops!");
console.log("done");
}
while(value) {
break;
console.log("done");
}
throw new Error("Oops!");
console.log("done");
function baz() {
if (Math.random() < 0.5) {
return;
} else {
throw new Error();
}
console.log("done");
}
for (;;) {}
console.log("done");
由于 JavaScript 函数和变量提升，此规则的正确代码示例：
¥Examples of correct code for this rule, because of JavaScript function and variable hoisting:
/*eslint no-unreachable: "error"*/
function foo() {
return bar();
function bar() {
return 1;
}
}
function bar() {
return x;
var x;
}
switch (foo) {
case 1:
break;
var x;
}
此规则的其他错误代码示例：
¥Examples of additional incorrect code for this rule:
/*eslint no-unreachable: "error"*/
class C extends B {
#x; // unreachable
#y = 1; // unreachable
a; // unreachable
b = 1; // unreachable
constructor() {
return {};
}
}
此规则的附加正确代码示例：
¥Examples of additional correct code for this rule:
/*eslint no-unreachable: "error"*/
class D extends B {
#x;
#y = 1;
a;
b = 1;
constructor() {
super();
}
}
class E extends B {
#x;
#y = 1;
a;
b = 1;
// implicit constructor always calls `super()`
}
class F extends B {
static #x;
static #y = 1;
static a;
static b = 1;
constructor() {
return {};
}
}
由 TypeScript 处理
使用 TypeScript 时禁用此规则是安全的，因为 TypeScript 的编译器强制执行此检查。
TypeScript 必须配置为 allowUnreachableCode: false，才能将无法访问的代码视为错误。
版本
此规则是在 ESLint v0.0.6 中引入。