mirror of
https://git.proxmox.com/git/pve-eslint
synced 2025-10-06 02:14:51 +00:00
eb39fafa4f
includes a (minimal) working wrapper Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>
108 lines
2.7 KiB
Markdown
108 lines
2.7 KiB
Markdown
# Disallow use of the void operator. (no-void)
|
|
|
|
The `void` operator takes an operand and returns `undefined`: `void expression` will evaluate `expression` and return `undefined`. It can be used to ignore any side effects `expression` may produce:
|
|
|
|
The common case of using `void` operator is to get a "pure" `undefined` value as prior to ES5 the `undefined` variable was mutable:
|
|
|
|
```js
|
|
// will always return undefined
|
|
(function(){
|
|
return void 0;
|
|
})();
|
|
|
|
// will return 1 in ES3 and undefined in ES5+
|
|
(function(){
|
|
undefined = 1;
|
|
return undefined;
|
|
})();
|
|
|
|
// will throw TypeError in ES5+
|
|
(function(){
|
|
'use strict';
|
|
undefined = 1;
|
|
})();
|
|
```
|
|
|
|
Another common case is to minify code as `void 0` is shorter than `undefined`:
|
|
|
|
```js
|
|
foo = void 0;
|
|
foo = undefined;
|
|
```
|
|
|
|
When used with IIFE (immediately-invoked function expression), `void` can be used to force the function keyword to be treated as an expression instead of a declaration:
|
|
|
|
```js
|
|
var foo = 1;
|
|
void function(){ foo = 1; }() // will assign foo a value of 1
|
|
+function(){ foo = 1; }() // same as above
|
|
```
|
|
|
|
```
|
|
function(){ foo = 1; }() // will throw SyntaxError
|
|
```
|
|
|
|
Some code styles prohibit `void` operator, marking it as non-obvious and hard to read.
|
|
|
|
## Rule Details
|
|
|
|
This rule aims to eliminate use of void operator.
|
|
|
|
Examples of **incorrect** code for this rule:
|
|
|
|
```js
|
|
/*eslint no-void: "error"*/
|
|
|
|
void foo
|
|
void someFunction();
|
|
|
|
var foo = void bar();
|
|
function baz() {
|
|
return void 0;
|
|
}
|
|
```
|
|
|
|
## Options
|
|
|
|
This rule has an object option:
|
|
|
|
* `allowAsStatement` set to `true` allows the void operator to be used as a statement (Default `false`).
|
|
|
|
### allowAsStatement
|
|
|
|
When `allowAsStatement` is set to true, the rule will not error on cases that the void operator is used as a statement, i.e. when it's not used in an expression position, like in a variable assignment or a function return.
|
|
|
|
Examples of **incorrect** code for `{ "allowAsStatement": true }`:
|
|
|
|
```js
|
|
/*eslint no-void: ["error", { "allowAsStatement": true }]*/
|
|
|
|
var foo = void bar();
|
|
function baz() {
|
|
return void 0;
|
|
}
|
|
```
|
|
|
|
Examples of **correct** code for `{ "allowAsStatement": true }`:
|
|
|
|
```js
|
|
/*eslint no-void: ["error", { "allowAsStatement": true }]*/
|
|
|
|
void foo;
|
|
void someFunction();
|
|
```
|
|
|
|
## When Not To Use It
|
|
|
|
If you intentionally use the `void` operator then you can disable this rule.
|
|
|
|
## Further Reading
|
|
|
|
* [Mozilla Developer Network](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/void)
|
|
* [Bad Parts: Appendix B - JavaScript: The Good Parts by Douglas Crockford](https://oreilly.com/javascript/excerpts/javascript-good-parts/bad-parts.html)
|
|
|
|
## Related Rules
|
|
|
|
* [no-undef-init](no-undef-init.md)
|
|
* [no-undefined](no-undefined.md)
|