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5.7.2 debugger

If the object o has a property x, then this code assigns the value 1 to that property. But if x is not defined in o, this code is the same as x = 1 without the with statement. It assigns to a local or global variable named x, or creates a new property of the global object. A with statement provides a shortcut for reading properties of o, but not for creating new properties of o.


5.7.2 debugger

The debugger statement normally does nothing. If, however, a debugger program is available and is running, then an implementation may (but is not required to) perform some kind of debugging action. In practice, this statement acts like a breakpoint: execution of JavaScript code stops and you can use the debugger to print variables’ values,

5.7 Miscellaneous Statements | 109

examine the call stack, and so on. Suppose, for example, that you are getting an exception in your function f()because it is being called with an undefined argument, and you can’t figure out where this call is coming from. To help you in debugging this problem, you might alter f() so that it begins like this:

function f(o) {

if (o === undefined) debugger; // Temporary line for debugging purposes

... // The rest of the function goes here.

}

Now, when f() is called with no argument, execution will stop, and you can use the debugger to inspect the call stack and find out where this incorrect call is coming from.

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