mirror of
https://github.com/alrayyes/wiki.git
synced 2024-11-23 03:56:23 +00:00
41 lines
1 KiB
Markdown
41 lines
1 KiB
Markdown
---
|
|
id: c5fef6b1-c659-42ef-8b51-7657df6743e8
|
|
title: JavaScript Strict Mode
|
|
---
|
|
|
|
# Description
|
|
|
|
[Strict
|
|
mode](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Strict_mode)
|
|
makes several changes to normal JavaScript semantics:
|
|
|
|
- Eliminates some JavaScript silent errors by changing them to throw
|
|
errors.
|
|
- Fixes mistakes that make it difficult for JavaScript engines to
|
|
perform optimizations: strict mode code can sometimes be made to run
|
|
faster than identical code that's not strict mode.
|
|
- Prohibits some syntax likely to be defined in future versions of
|
|
ECMAScript.
|
|
|
|
``` javascript
|
|
function canYouSpotTheProblem() {
|
|
"use strict";
|
|
for (counter = 0; counter < 10; counter++) {
|
|
console.log("Happy happy");
|
|
}
|
|
}
|
|
|
|
canYouSpotTheProblem();
|
|
// → ReferenceError: counter is not defined
|
|
```
|
|
|
|
In strict mode the \`this\` binding holds the value \`undefined\` in
|
|
functions that are not called as methods:
|
|
|
|
``` javascript
|
|
"use strict";
|
|
|
|
function doSomething() {
|
|
console.log(this)
|
|
}
|
|
```
|