Debugging in JavaScript

Debugging in JavaScript means finding and fixing mistakes in your code. It involves using tools like browser consoles, debuggers, and logs to check how the code runs, follow its steps, and fix any problems.

JavaScript Debugging Example

Here, we will find errors using the built-in web browser debugger. To debug, we can use these methods:

  • Console Logging: Add console.log() statements in your code to see what is happening at different points.Breakpoints: Set breakpoints in the browser’s developer tools to pause the code at specific lines and inspect variables.Step Through Code: Use the debugger to step through your code line by line to see how it executes.Inspect Variables: Check the values of variables at different points to make sure they are what you expect.Error Messages: Look at the error messages in the console to understand where the code is failing.
  • Using console.log() method:

    The console.log() method shows results in the browser’s console. If there’s a mistake in the code, it generates an error message.

    Let’s see the simple example to print the result on console.

    x = 10;  
    y = 15;  
    z = x + y;  
    console.log(a);//a is not intialized  


    To open the console on browser, press F12 key.

    Using debugger keyword:-

    Using the debugger keyword in JavaScript pauses the code execution at the point where it’s placed. This allows you to inspect the current state of the program. Here’s how to use it:

    Insert debugger Keyword: Place the debugger keyword in your code where you want to pause.

    Open Developer Tools: Open the browser’s developer tools (usually by pressing F12 or right-clicking and selecting “Inspect”).

    Run the Code: Execute the code. When the browser hits the debugger keyword, it will pause execution.

    Inspect the Code: While paused, you can inspect variables, step through the code, and see what is happening at that point.

    JavaScript Hoisting

    JavaScript hoisting is a behavior where variable and function declarations are moved to the top of their containing scope during the compilation phase. This means you can use variables and functions before you declare them in your code. However, only the declarations are hoisted, not the initializations.

    Here’s a simple explanation:

    Variable Hoisting:

    • Only the declaration is hoisted, not the assignment
    • If you try to use a variable before it is declared and initialized, it will be undefined

    The above code is interpreted by JavaScript as:

    Function Hoisting:

    • Function declarations are hoisted with their definitions.
    • You can call a function before it is declared

    The above code works because the function declaration and its definition are both hoisted to the top.

    Let and Const Hoisting:

    • Variables declared with let and const are also hoisted, but they are not initialized.
    • They are placed in a “temporal dead zone” until the actual declaration is encountered in the code.