Whenever I come back to pure Javascript it's a bit uncomfortable because Javascript has some different rules from most language about defining variables. This post is meant to be a quick refresher on defining variables in Javascript.
Javascript Scope
Remember that scope of the variable refers to where in the code it has access to the variable. In Javascript we cannot use access modifiers like public or protected as in other languages.
Local Javascript Variables
Variables that are defined inside of a function are only available to be used inside of that function. These are called local variables, and in general they are good to use because they get garbage collected once the function ends (sort of). Local variables would make a good choice should only be used on temporary variables, intermediate calculations, and things that aren't needed later in the program. Here's an example where material is a local variable:
// code here can not use material function myFunction() { var material = "sand"; // code here can use material }
Remember, this is pure javascript so don't go trying to tell the JS interpreter that this is a String (even though it is) or use data types when defining your variables!
Global Javascript Variables
Just define a variable outside of a function but inside of the class, and it will be available inside of all function in that class. In the example below, the variable material is now available throughout the entire class:
var material = "sand"; // code here can use material function myFunction() { // code here can use material }
Automatically Global Variables
Although this has undoubtably, caused a lot of face-palming over the years, Javascript has an interesting little "feature" that occurs when you omit the var keyword. If you assign a value to a variable that has not been declared without the var keyword then it becomes global automatically. Don't ask me why; that's just how it is! If you really hate it that much, switch to Typescript, but it is what it is. Here's an example where the material variable automatically takes global scope:
// code here can use material function myFunction() { material = "sand"; // code here can use material }
Sharing a "Public Javascript Variable" with Another Class
Once you start getting familiar with Javascript and are itching to build a more than a few functions you'll want to put on your OOP hat and break the code into separate files. I would say separate classes, but up until ES6 there were no concept of classes in Javascript. For that reason I'm going for an old-school route of defining a Java file with it's main function. Let's say we have a class, CountManager, and it needs to read the value of the variable age in a class called Person.
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