Strict mode is a feature in JavaScript introduced in ECMAScript 5 (ES5) that allows you to place a program or a function in a "strict" operating context. When you use strict mode, it enforces stricter parsing and error handling in your code, catching common coding mistakes and preventing certain actions that may be error-prone or have undesirable behavior in JavaScript.
To enable strict mode, you can add the following line at the beginning of a script or function:
"use strict";
or:
function myFunction() {
"use strict";
// Function code in strict mode
}
Here are some aspects of strict mode:
-
Error Reporting: It makes it easier to write "secure" JavaScript by highlighting common mistakes as errors that would otherwise be ignored or fail silently in non-strict mode. For example, assigning values to undeclared variables, using reserved keywords (like
eval, arguments,etc.) as variable or function names, etc. - Preventing Global Scope Pollution: In strict mode, attempting to assign a value to an undeclared variable will throw an error. This helps prevent accidental creation of global variables.
-
Safer Code: Certain actions that are considered dangerous or deprecated are restricted or disallowed in strict mode, such as the use of
withstatement, which is disallowed in strict mode as it can lead to confusion and unintended side effects. - Better Performance: In some cases, strict mode code can be optimized by the JavaScript engine for better performance.
Using strict mode is a good practice as it helps in writing more robust and maintainable code by catching common errors and discouraging the use of problematic or error-prone features. However, it's important to note that enabling strict mode may change the behavior of existing code, especially if it relies on features that are disallowed or modified in strict mode
