mirror of
https://git.proxmox.com/git/pve-eslint
synced 2025-10-05 11:41:00 +00:00
eb39fafa4f
includes a (minimal) working wrapper Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>
174 lines
3.6 KiB
Markdown
174 lines
3.6 KiB
Markdown
# disallow variable declarations from shadowing variables declared in the outer scope (no-shadow)
|
|
|
|
Shadowing is the process by which a local variable shares the same name as a variable in its containing scope. For example:
|
|
|
|
```js
|
|
var a = 3;
|
|
function b() {
|
|
var a = 10;
|
|
}
|
|
```
|
|
|
|
In this case, the variable `a` inside of `b()` is shadowing the variable `a` in the global scope. This can cause confusion while reading the code and it's impossible to access the global variable.
|
|
|
|
## Rule Details
|
|
|
|
This rule aims to eliminate shadowed variable declarations.
|
|
|
|
Examples of **incorrect** code for this rule:
|
|
|
|
```js
|
|
/*eslint no-shadow: "error"*/
|
|
/*eslint-env es6*/
|
|
|
|
var a = 3;
|
|
function b() {
|
|
var a = 10;
|
|
}
|
|
|
|
var b = function () {
|
|
var a = 10;
|
|
}
|
|
|
|
function b(a) {
|
|
a = 10;
|
|
}
|
|
b(a);
|
|
|
|
if (true) {
|
|
let a = 5;
|
|
}
|
|
```
|
|
|
|
## Options
|
|
|
|
This rule takes one option, an object, with properties `"builtinGlobals"`, `"hoist"` and `"allow"`.
|
|
|
|
```json
|
|
{
|
|
"no-shadow": ["error", { "builtinGlobals": false, "hoist": "functions", "allow": [] }]
|
|
}
|
|
```
|
|
|
|
### builtinGlobals
|
|
|
|
The `builtinGlobals` option is `false` by default.
|
|
If it is `true`, the rule prevents shadowing of built-in global variables: `Object`, `Array`, `Number`, and so on.
|
|
|
|
Examples of **incorrect** code for the `{ "builtinGlobals": true }` option:
|
|
|
|
```js
|
|
/*eslint no-shadow: ["error", { "builtinGlobals": true }]*/
|
|
|
|
function foo() {
|
|
var Object = 0;
|
|
}
|
|
```
|
|
|
|
### hoist
|
|
|
|
The `hoist` option has three settings:
|
|
|
|
* `functions` (by default) - reports shadowing before the outer functions are defined.
|
|
* `all` - reports all shadowing before the outer variables/functions are defined.
|
|
* `never` - never report shadowing before the outer variables/functions are defined.
|
|
|
|
#### hoist: functions
|
|
|
|
Examples of **incorrect** code for the default `{ "hoist": "functions" }` option:
|
|
|
|
```js
|
|
/*eslint no-shadow: ["error", { "hoist": "functions" }]*/
|
|
/*eslint-env es6*/
|
|
|
|
if (true) {
|
|
let b = 6;
|
|
}
|
|
|
|
function b() {}
|
|
```
|
|
|
|
Although `let b` in the `if` statement is before the *function* declaration in the outer scope, it is incorrect.
|
|
|
|
Examples of **correct** code for the default `{ "hoist": "functions" }` option:
|
|
|
|
```js
|
|
/*eslint no-shadow: ["error", { "hoist": "functions" }]*/
|
|
/*eslint-env es6*/
|
|
|
|
if (true) {
|
|
let a = 3;
|
|
}
|
|
|
|
let a = 5;
|
|
```
|
|
|
|
Because `let a` in the `if` statement is before the *variable* declaration in the outer scope, it is correct.
|
|
|
|
#### hoist: all
|
|
|
|
Examples of **incorrect** code for the `{ "hoist": "all" }` option:
|
|
|
|
```js
|
|
/*eslint no-shadow: ["error", { "hoist": "all" }]*/
|
|
/*eslint-env es6*/
|
|
|
|
if (true) {
|
|
let a = 3;
|
|
let b = 6;
|
|
}
|
|
|
|
let a = 5;
|
|
function b() {}
|
|
```
|
|
|
|
#### hoist: never
|
|
|
|
Examples of **correct** code for the `{ "hoist": "never" }` option:
|
|
|
|
```js
|
|
/*eslint no-shadow: ["error", { "hoist": "never" }]*/
|
|
/*eslint-env es6*/
|
|
|
|
if (true) {
|
|
let a = 3;
|
|
let b = 6;
|
|
}
|
|
|
|
let a = 5;
|
|
function b() {}
|
|
```
|
|
|
|
Because `let a` and `let b` in the `if` statement are before the declarations in the outer scope, they are correct.
|
|
|
|
### allow
|
|
|
|
The `allow` option is an array of identifier names for which shadowing is allowed. For example, `"resolve"`, `"reject"`, `"done"`, `"cb"`.
|
|
|
|
Examples of **correct** code for the `{ "allow": ["done"] }` option:
|
|
|
|
```js
|
|
/*eslint no-shadow: ["error", { "allow": ["done"] }]*/
|
|
/*eslint-env es6*/
|
|
|
|
import async from 'async';
|
|
|
|
function foo(done) {
|
|
async.map([1, 2], function (e, done) {
|
|
done(null, e * 2)
|
|
}, done);
|
|
}
|
|
|
|
foo(function (err, result) {
|
|
console.log({ err, result });
|
|
});
|
|
```
|
|
|
|
## Further Reading
|
|
|
|
* [Variable Shadowing](https://en.wikipedia.org/wiki/Variable_shadowing)
|
|
|
|
## Related Rules
|
|
|
|
* [no-shadow-restricted-names](no-shadow-restricted-names.md)
|