What is Use Strict ?

In JavaScript, it's important to write code that's not only functional but also maintainable and easy to read. One way to achieve this is by using strict mode. In this article, we'll explain what strict mode is, how it works, and provide some examples of how to use it.

What is Strict Mode?

Strict mode is a special mode that's available in JavaScript to help developers write better code. It's a way of telling the JavaScript engine to enforce stricter rules when interpreting your code. When you enable strict mode, the JavaScript engine will throw more errors and prevent certain types of behavior that are not allowed in normal mode.

How to Enable Strict Mode?

To enable strict mode, simply include the following line at the beginning of your JavaScript file or within a function:

"use strict";        

By adding this line of code, you're telling the JavaScript engine to enter strict mode and enforce stricter rules when interpreting your code.

Examples of Strict Mode

Let's look at some examples of how strict mode can help us write better code.

1. Preventing Undeclared Variables

In normal mode, if you try to assign a value to an undeclared variable, JavaScript will create a new global variable with that name. This can lead to unexpected behavior and bugs. However, in strict mode, this behavior is not allowed. Here's an example:

function example() {
? "use strict";
? myVar = 10; // Throws an error in strict mode
}        

In this example, we're trying to assign a value to a variable called myVar without declaring it first. In normal mode, this would create a new global variable. However, in strict mode, this behavior is not allowed, and an error is thrown.

1. Preventing Duplicate Parameters

In normal mode, you can define a function with duplicate parameters without any issues. However, in strict mode, this behavior is not allowed. Here's an example:

function example(a, b, a) {
? "use strict";
? // Throws an error in strict mode
}        

In this example, we're defining a function with two parameters called a and b. However, we're also defining a third parameter called a, which is a duplicate. In normal mode, this would work without any issues. However, in strict mode, this behavior is not allowed, and an error is thrown.

1. Preventing Octal Literals

In normal mode, you can define a number using an octal literal by prefixing it with a zero (e.g. 012). However, in strict mode, this behavior is not allowed. Here's an example:

function example() {
? "use strict";
? var num = 012; // Throws an error in strict mode
}        

In this example, we're defining a variable called num and assigning it the value 012, which is an octal literal. In normal mode, this would work without any issues. However, in strict mode, this behavior is not allowed, and an error is thrown.

Conclusion

In conclusion, strict mode is a powerful feature in JavaScript that can help you write better code. By enabling strict mode, you can prevent unexpected behavior, catch errors early, and make your code more maintainable. It's recommended to use strict mode in all your JavaScript files and functions to ensure that your code is as robust as possible.