JavaScript Breakpoints

Breakpoints in JavaScript serve as vital instruments during the debugging phase. The primary purpose of utilizing breakpoints in JavaScript stems from the fact that while developing our program's code, we often come across various syntax errors and logical discrepancies. Consequently, the expected output may not be generated by the code in such situations.

In order to identify the locations within our code that are causing issues and to resolve them for successful output, we engage in debugging the entire codebase. This involves monitoring and validating the execution flow by pausing at each stage of the execution process.

Breakpoints serve a crucial role in the debugging process across various programming languages, utilizing a range of specific breakpoint commands. In particular, breakpoints halt the execution flow, allowing for a thorough examination of each step to identify potential errors.

How to Set Breakpoints

To establish breakpoints within the debugger, one can easily place them on the left side of the debugger interface for the JavaScript code. These breakpoints may be visually represented as either red or blue dots, contingent upon the specific tool being utilized. At each breakpoint, the debugging tool will halt the execution process during runtime, allowing for the inspection of variable values. The primary purpose of incorporating breakpoints in the runtime process stems from the fact that issues and the underlying reasons for code failures are typically identifiable only during execution. Generally, errors in the code are not disclosed, and logs are also made available exclusively at runtime.

Breakpoint Examples

1. Visual Studio Code (VS Code):

Visual Studio Code has become the preferred web browser for numerous developers, primarily due to its user-friendly features that simplify navigation and error inspection within the code. Breakpoints can be easily implemented, and JavaScript developers can take full advantage of this functionality.

To access breakpoints for JavaScript files within Visual Studio Code, begin by opening the file containing your JavaScript code. To set the breakpoints, simply click on the margin next to the line number of the code where you wish to place the breakpoint. This action will create a red dot indicating the breakpoint's position. You can then effortlessly debug your code by either pressing the F5 key or by navigating to the menu and selecting Run followed by Start Debugging.

Example:

Code:

function multiplication( a, b, c ) {
    return a * b*c ;
}

let res = multiplication( 43, 9 ,2 );
console.log( res );
// Simply set a breakpoint on the return statement to verify the result

Output:

2. Browser Developer Tools Breakpoints

In contemporary software development, we frequently rely on browser tools for various processes. Well-known browsers such as Chrome, Microsoft Edge, Mozilla Firefox, and others offer robust developer tools. These tools are designed to facilitate the setting of breakpoints in a clear and uncomplicated way.

To make use of breakpoints within the browser's developer tools, you can either right-click or press F12 to access a variety of options. From this menu, select "Inspect." This action will open a new tab and direct you to the "Sources" section. Next, locate your specific JavaScript file. You can then establish breakpoints by clicking on the line number of the code where you wish to pause execution.

Example:

Code:

for (let i = 1; i < 15; i++) {
    console.log(i);
    // we can set the conditional breakpoint here by the condition: i === 7
}

Output:

3. Breakpoints using debugger statement

In JavaScript files, breakpoints can be implemented through the use of built-in commands. This functionality can be accomplished using the debugger statement that is included in JavaScript. When the JavaScript engine encounters the debugger within the code, it will halt execution, at which point the debugger will activate and become accessible for use.

Example:

Code:

function calculateSum(num1, num2) {
    let result = num1 + num2;
    debugger; // Execution will get paused here in case the debugger is open
    return result;
}

let sum = calculateSum(5, 15);
console.log(sum);

Output:

In the code provided for determining the sum of two numbers, when the executor encounters the debugger statement, it promptly halts the execution and verifies whether the debugger is currently active.

There are several methods through which breakpoints can be utilized in JavaScript. Additionally, there are various other applications for breakpoints, such as the implementation of conditional breakpoints within browser development tools and other improvised techniques, among others.