How to see Javascript stack of a website?

Let's say I am visiting CNN, and they use javascript as we know. They initializ开发者_开发知识库e some variables and change it during my visit. How can I watch what values these variables are getting?

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Install firebug and use the script tab. You can set breakpoints, step through code and more.

If you are not using FF, you can use firebuglite.

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IE8 and above have similar built in dev tools easily accessible by pressing F12.

Chrome and Safari have such built in tools too, and so does the latest version of Opera.