5. Global environment

So far, we've covered Javascript's key words, a few essential functions and the notions of scope and environment. What is the global environment and what does it contain? The answer depends on the particular implementation of Javascript.

In a browser, Javascript runs in a restricted context for security reasons. Indeed, allowing Javascript in your browser means allowing code written from who knows where to run in your browser and therefore on your machine. We can no longer cite the attacks where such code could steal sensitive files, send spam, inspect a company's internal network or spy on other Javascript code in order to find bank card numbers or passwords. Browsers have gone to great lengths to limit these risks and, as a result, provide feature-restricted libraries: it is thus not possible for a Javascript program running in a browser to read the user's hard...