How Does JavaScript Work?
javascript is a full-fledged dynamic programming language that, when applied to HTML, can add animation and interactivity to web pages. In fact, almost anything that moves or changes on a website without you having to manually refresh your browser is the work of javascript. It’s also responsible for things like autocomplete text suggestions and image slideshows.
The first thing to understand about javascript is how it executes scripts. It’s a client-side programming language, meaning it’s run directly within your web browser. This differs from server-side languages, which must be run on a separate machine.
When you open a web page or app that contains javascript, the engine inside your browser starts up and begins to read line by line of code. It starts at the top of the page and works its way down, executing each function in turn. If it encounters an error, it will stop and return an error to the developer console (see below).
As you progress through the code, you will notice that variables are used for each operation. Each variable is represented by a prototype, which is essentially a container for the values that the variable represents. For example, the prototype for a number is Number. Whenever you perform a number operation on the prototype, such as concatenation or subtraction, JavaScript will cast the value to a string for that particular operation. This happens to prevent things like string concatenation or number subtraction from becoming inexactly equal to each other, which can cause confusion for beginners.
Once the code is complete, it’s time to implement and run the function that was called from the js script. This is done by pushing a new stack frame onto the Call Stack. This stack frame holds information about the current function, including its arguments and local variables. When the function returns, its stack frame is popped off the Call Stack and execution continues at the return address specified by the function.
While this may seem like a lot of steps, it actually happens very quickly. The reason is that the engine in your browser is running a very fast virtual machine, and it knows that it can trust the code to run properly. This makes coding in JavaScript more efficient than coding in other languages, which require the virtual machine to compile the code into a native executable at the point of execution.
Once you’ve mastered these basic concepts, you can start working with some more complicated examples. In the next section, we’ll look at some more advanced javascript code that takes an input from the user, calculates the square of it and displays the answer to the user on screen. This example will utilize a few other concepts, such as vars, functions and the global execution context. We’ll also see some of the errors that might occur and how to resolve them. By the end, you will be ready to write and test your own javascript code!