Javascript: Why 'use strict';

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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