Every concept in Javascript has too much information to keep in mind. Even "use strict;" as well. I can write lengthy article on it but I am a kind of guy usually ignore lengthy theoretical articles. So, this time I want to write article in different way but like one stop for "use strict;". No further words. Let's start:
What is "use strict;"?
To indicate code should run in strict mode - Thatz it. Yes 😊
How to use?
Everywhere in article writing it as "use strict;". Just place the same to the beginning of function or script.
When it is introduced in Javascript?
Do we really required?🧐 anyhow, In ES 5.
Please don't ask me, who introduced it. 😛
why do I use?
It makes to write secure Javascript. Short answers are not accepted for questions starting with Why😳.
Alright, Let's go deep but no theory.
| S.No | Action | Example | Strict Mode | Non - Strict Mode | Fix |
|---|---|---|---|---|---|
| 1 | Using variable without declaring it |
|
Uncaught ReferenceError: a is not defined | 3.14 |
|
| 2 | Deleting a variable |
|
Uncaught SyntaxError: Delete of an unqualified identifier in strict mode. | false | It can't be deleted. Variables created without var, let & const are deleted using delete. |
| 3 | Duplicate function params |
|
Uncaught SyntaxError: Duplicate parameter name not allowed in this context | 10 10 |
|
| 4 | Octal numeric literals |
|
Uncaught SyntaxError: Octal literals are not allowed in strict mode. | 8 |
|
| 5 | Using variable name as eval or arguments |
|
Uncaught SyntaxError: Unexpected eval or arguments in strict mode | 10 20 |
|
| 6 | `this` inside function - refers to the object that called the function. |
|
undefined | Returns window object: Window {0: Window, 1: Window, 2: global,...... | Avoid using this inside functions to not to expose window object. |
| 7 | Creating variable with `eval` |
|
Uncaught ReferenceError: a is not defined | 10 | Avoid using eval. |
| 8 | Using `with` statement |
|
Uncaught SyntaxError: Strict mode code may not include a with statement | 20 | Avoid using it |
| 9 | Deleting undeletable property |
|
Uncaught TypeError: Cannot delete property 'prototype' of function Object() { [native code] } at :2:1 | false | Avoid it |
| 10 | Using Octal Escape characters |
|
Uncaught SyntaxError: Octal escape sequences are not allowed in strict mode. | Returns nothing | Avoid it |
| 11 | Writing to read only property |
|
Uncaught TypeError: Cannot assign to read only property 'a' of object '#' | 10 |
|
| 12 | Writing to get only property |
|
Uncaught TypeError: Cannot set property test of # which has only a getter | FIRST |
|
| 13 | Using variable as reserved keywords |
|
Uncaught SyntaxError: Unexpected strict mode reserved word | 10 | Avoid using reserved keywords as variables |
Oops, it took whole day to write. Anyhow, please do comment if I miss any or in case of improvements.
Thanks.
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