What is JavaScript?
If you are taking this course, you know that JavaScript is a popular client-side programming language. Client-side programs run on your computer's web browser. So, where can you see JavasScript on the web? When you visit a website and submit a form, that's JavaScript. The language is easy to use and learn. This article introduces several features of the language and some of the things you can do with it.
Interpreted versus compiled code
You might hear the terms interpreted and compiled in the context of programming. In interpreted languages, the code is run from top to bottom and the result of running the code is immediately returned. You don't have to transform the code into a different form before the browser runs it. The code is received in its programmer-friendly text form and processed directly from that.
Compiled languages on the other hand are transformed (compiled) into another form before they are run by the computer. For example, C/C++ are compiled into machine code that is then run by the computer. The program is executed from a binary format, which was generated from the original program source code.
JavaScript is a lightweight interpreted programming language. The web browser receives the JavaScript code in its original text form and runs the script from that. From a technical standpoint, most modern JavaScript interpreters actually use a technique called just-in-time compiling to improve performance; the JavaScript source code gets compiled into a faster, binary format while the script is being used, so that it can be run as quickly as possible. However, JavaScript is still considered an interpreted language, since the compilation is handled at run time, rather than ahead of time.
There are advantages to both types of language, but we won't discuss them right now.