Introduction
“Use strict” is a directive that is used to enable strict mode in JavaScript. Strict mode is a way to opt-in to a restricted variant of JavaScript that helps to catch common coding mistakes and prevent them from becoming bugs. It is a way to ensure that code is written in a more secure and reliable manner. The reasoning behind using strict mode is to help developers write better code and to help prevent errors and potential security issues.
Solution
“use strict” is a directive that enables strict mode in JavaScript. Strict mode is a way to opt in to a restricted variant of JavaScript that eliminates some of the silent errors that can occur in regular JavaScript. It also throws more exceptions, which makes it easier to spot and debug errors. The main purpose of strict mode is to make it easier to write secure and reliable code. Strict mode also helps to prevent accidental global variable declarations, which can lead to unexpected behavior and security issues.
Update for ES6 modules
Inside native ECMAScript modules (with import and export statements) and ES6 classes, strict mode is always enabled and cannot be disabled.
Original answer
This article about Javascript Strict Mode might interest you: John Resig – ECMAScript 5 Strict Mode, JSON, and More
To quote some interesting parts:
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.
And:
Strict mode helps out in a couple ways:
- It catches some common coding bloopers, throwing exceptions.
- It prevents, or throws errors, when relatively “unsafe” actions are taken (such as gaining access to the global object).
- It disables features that are confusing or poorly thought out.
Also note you can apply “strict mode” to the whole file… Or you can use it only for a specific function (still quoting from John Resig’s article):
// Non-strict code...
(function(){
"use strict";
// Define your library strictly...
})();
// Non-strict code...
Which might be helpful if you have to mix old and new code ?
So, I suppose it’s a bit like the "use strict" you can use in Perl (hence the name?): it helps you make fewer errors, by detecting more things that could lead to breakages.
Strict mode is now supported by all major browsers.
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solved What does “use strict” do in JavaScript, and what is the reasoning behind it?
What Does “use Strict” Do in JavaScript, and What is the Reasoning Behind It?
The “use strict” directive is a way to enforce stricter parsing and error handling in your JavaScript code. It is a literal expression, not a statement, so it must be included within a script tag or a function block. When used, it enables a set of restrictions that throw more exceptions and disallow certain syntax. The reasoning behind using “use strict” is to help developers write more secure and reliable code.
When “use strict” is enabled, it prevents the use of undeclared variables. This means that all variables must be declared before they can be used. This helps to prevent accidental global variables, which can cause unexpected behavior and errors. It also disallows the use of certain syntax, such as the use of the with statement, which can lead to confusion and errors.
Another benefit of using “use strict” is that it helps to prevent the use of certain features that are considered to be bad practice. For example, it disallows the use of octal syntax, which can lead to confusion and errors. It also disallows the use of the eval() function, which can be used to inject malicious code into your application.
Overall, the use of “use strict” helps to ensure that your code is more secure and reliable. It helps to prevent the use of certain features that can lead to confusion and errors, and it helps to prevent the use of undeclared variables. By using “use strict”, you can help to ensure that your code is more secure and reliable.