javascript

Chapter 14: Error Handling and Debugging
sign appears next to it that, when clicked, shows all of the properties and methods of the object. An
object value can also be clicked in the Watch tab to inspect the object closer. When an object value is
clicked, it opens the DOM tab, which lists all of the properties and methods of the object in a wider view.
Watches
Watches are added by clicking on the yellow area at the top of the Watch tab and typing in a variable
name. When a watch is added, it is displayed with a gray background at the top of the Watch tab, and
local variables are displayed with white backgrounds beneath it. Whenever the watch is in scope, the
variable ’ s value is filled in appropriately; when the variable is out of scope, an error is displayed for the
value. Moving your cursor over a watch reveals a red X button that can be used to delete the watch. See
Figure 14 - 22 .
Figure 14-22
In Figure 14 - 22 , there are two watches: type and window . They are at the top of the Watch tab, and the
local variables appear beneath them. Note that the local variable type and the watch type are both
inspecting the same variable.
The JavaScript Console
The JavaScript console is on the Console tab as opposed to the Script tab on which the debugger resides. The
console was used earlier in the chapter to output messages, but it can also be used as a command line for
running JavaScript code within the context of the page. You need only type in some JavaScript code and
press Enter to execute any arbitrary code and see the result output on the console. See Figure 14-23 .
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