优先使用 const
注意:此规则是
推荐
规则集的一部分。在
deno.json
中启用完整集合{ "lint": { "rules": { "tags": ["recommended"] } } }
使用 Deno CLI 启用完整集合
deno lint --rules-tags=recommended
通过将其添加到
deno.json
中的include
或exclude
数组,可以将此规则明确地包含或排除在当前标签的规则集中。{ "lint": { "rules": { "include": ["prefer-const"], "exclude": ["prefer-const"] } } }
自 ES2015 起,JavaScript 支持使用let
和const
声明变量。如果变量用let
声明,则它们是可变的;我们可以在之后为其设置其他值。同时,如果用const
声明,则它们是不可变的;我们无法对其进行重新赋值。
通常,为了使代码库更健壮、更易于维护和更具可读性,强烈建议尽可能使用const
而不是let
。可变变量越少,在阅读代码时就越容易跟踪变量状态,因此编写出有缺陷代码的可能性就越小。因此,此 lint 规则会检查是否存在本可以声明为const
而非let
的变量。
请注意,此规则不检查var
变量。相反,no-var
规则负责检测和警告var
变量。
无效示例
let a = 0;
let b = 0;
someOperation(b);
// `const` could be used instead
for (let c in someObject) {}
// `const` could be used instead
for (let d of someArray) {}
// variable that is uninitialized at first and then assigned in the same scope is NOT allowed
// because we could simply write it like `const e = 2;` instead
let e;
e = 2;
有效示例
// uninitialized variable is allowed
let a;
let b = 0;
b += 1;
let c = 0;
c = 1;
// variable that is uninitialized at first and then assigned in the same scope _two or more times_ is allowed
// because we cannot represent it with `const`
let d;
d = 2;
d = 3;
const e = 0;
// `f` is mutated through `f++`
for (let f = 0; f < someArray.length; f++) {}
// variable that is initialized (or assigned) in another scope is allowed
let g;
function func1() {
g = 42;
}
// conditionally initialized variable is allowed
let h;
if (trueOrFalse) {
h = 0;
}