What is a watch expression and how do you use it?

2 How to add watch expressions

To add watch expressions to your debugging tools, you need to follow these general steps. First, you need to open your debugging tool of choice and locate the watch panel or window. This is usually found in the same area as the call stack, breakpoints, and local variables. Second, you need to enter the code that you want to watch in the input field or click on the add button. You can enter any valid JavaScript code, such as variable names, expressions, or function calls. Third, you need to run or resume your code and observe the results of your watch expressions in the watch panel or window. You can also modify, delete, or disable your watch expressions as needed.

3 Tips and tricks for watch expressions

To make the most out of watch expressions, here are some tips and tricks that you can use. First, you can use watch expressions to evaluate complex or conditional expressions that are not easy to inspect with breakpoints or console.log statements. For example, you can use watch expressions to check the value of a loop counter, a string manipulation, or a boolean operation. Second, you can use watch expressions to call functions that are defined in your code or in the global scope. For example, you can use watch expressions to invoke a function that performs a calculation, a validation, or a manipulation on your data. Third, you can use watch expressions to access properties and methods of objects that are in scope. For example, you can use watch expressions to access the length, value, or type of an array, a string, or a number.

5 Examples of watch expressions

To illustrate how watch expressions work and how you can use them, let's consider the following HTML, CSS, and JavaScript code in your project. This code creates a div element that rotates back and forth between -180 and 180 degrees. You can add watch expressions to your browser's developer tools or your IDE to debug and understand this code, such as 'angle', 'speed * direction', 'container.style.transform', and 'rotate()'. These expressions will show the current values of the angle variable, the increment or decrement of the angle variable, the transform property of the div element, and the rotate function respectively. By experimenting with different values of speed and direction, you can observe how they affect the rotation of the div element.

6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?