What does 'use strict' mean in Javascript?

Question

JS 'use strict' meaning

Answer 1

TurtleShell in that case why is there even a non-strict or lenient mode? Will strict mode be the default in the future?

Answer 2

My opinion: It's nice to see because it makes devs declare variables (even guarding against redeclaration) instead of depending on JS auto-creating globals + hoisting.

Related functionality:
It enables 'let', 'const', `template` literals, classes + other things for my embedded webview (+ other people's too).
* Without it, many of the popular animations here are black on black, not-as-intended or don't work at all.
~ They don't necessarily show errors, but I have to guess if what I see / don't see might be JS compatibility bugs.
* Then when adding 'use strict' I often must correct declarations, but eventually I can test the code and comment.

As you might imagine, I don't like to 'add it later' quite as much. It really ought to be there from the start.

Answer 3

Thanks all for your answers. 👍

Answer 4

https://www.sololearn.com/Discuss/634966/?ref=app

Answer 5

Sonic because a lot of new and old code would be broken, you have to remember that JS powers probably around 95% of websites. As you probably also noticed "use strict"; is a string which wont cause errors on really old browsers.

Answer 6

Strict mode changes some previously-accepted mistakes into errors. JavaScript was designed to be easy for novice developers, and sometimes it gives operations which should be errors non-error semantics. Sometimes this fixes the immediate problem, but sometimes this creates worse problems in the future.

First, strict mode makes it impossible to accidentally create global variables.

Second, strict mode makes assignments which would otherwise silently fail to throw an exception. For example, NaN is a non-writable global variable. In normal code assigning to NaN does nothing; the developer receives no failure feedback. In strict mode assigning to NaN throws an exception. Any assignment that silently fails in normal code (assignment to a non-writable global or property, assignment to a getter-only property, assignment to a new property on a non-extensible object) will throw in strict mode:

Answer 7

http://lucybain.com/blog/2014/js-use-strict/
It basically puts your code in strict mode which forces you to write better code.

Answer 8

https://www.w3schools.com/js/js_strict.asp
A good tutorial by w3 schools

Answer 9

'use strict' mode is very important concept in javascript. if you are using it, it dosen't allow this as window keyword in your code unless you bind it.It actually make your code more secured because in non strict mode third person can easily access to your code because in non strict mode all your function variable get store in window.For example you make quiz application in non strict mode then user can easily access timer and he/she can make changes.I hope you will understand ,if still you have doubt text again.
Thanks

Answer 10

Strict mode in JavaScript. Strict Mode is a new feature in ECMAScript 5 that allows you to place a program, or a function, in a “strict” operating context. ... The statement “use strict”; instructs the browser to use the Strict mode, which is a reduced and safer feature set of JavaScript.
https://crbtech.in/java-training/java-certification-path-certified-made-easy/

Answer 11

Strict mode in JavaScript. Strict Mode is a new feature in ECMAScript 5 that allows you to place a program, or a function, in a “strict” operating context. This strict context prevents certain actions from being taken and throws more exceptions.
https://www.geeksforgeeks.org/strict-mode-javascript/
https://www.w3schools.com/js/js_strict.asp