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This article mainly introduces the example analysis of F12 debugger and debugger setting breakpoint in JavaScript. The article is very detailed and has certain reference value. Interested friends must finish reading it!

F12 debugger in JavaScript, debugger sets breakpoint

It is difficult to write JavaScript without a debugger.

Your code may contain syntax errors, or logic errors, which are difficult to diagnose.

Usually, nothing happens if the JavaScript code contains errors. There will be no error messages, and there will be no indication of errors.

Usually, every time you try to write new JavaScript code, an error may occur.

JavaScript Debugger

Finding errors in programming code is called code debugging.

Debugging is not easy. Fortunately, all modern browsers have built-in debuggers.

The built-in debugger can be turned on or off to force errors to be reported to the user.

Through the debugger, you can also set breakpoints (where code execution is interrupted) and check variables as the code executes.

Usually start the debugger in the browser with the F12 key, and then select console from the debugger menu.

Console.log () method

If your browser supports debugging, you can use console.log () to display the value of JavaScript in the debug window:

Example

My First Web Page

A = 5

B = 6

C = a + b

Console.log (c)

Set breakpoint

In the debug window, you can set breakpoints in your JavaScript code.

At each breakpoint, JavaScript stops execution so that you can check the value of JavaScript.

After checking the value, you can resume code execution.

Debugger keyword

The debugger keyword stops the execution of the JavaScript and calls the debug function, if any.

This is the same as setting breakpoints in the debugger.

If the debugger is not available, the debugger statement has no effect.

If the debugger is open, the code stops running before the third line is executed.

Example

Var x = 15 * 5

Debugger

Document.getElementbyId ("demo") [xss_clean] = x

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