Should I use a global variable and if not, what instead? (Javascript)

Global variables are, as you probably guessed, considered bad. Any other code on the page can modify them - often because another programmer accidentally picks the same name. You can try to mitigate this effect by choosing really strange names, but then you get a bunch of really strange names.

There are a lot of ways to minimize the number of global variables you create in JavaScript. One way is to store all your variables under a single object - that's what jQuery does (Technically jQuery uses two - $ and jQuery.)

If you know what you're doing, you often don't have to create any global variables - just wrap all your code in a function that you invoke immediately.

Bad example - pollutes the global namespace unnecessarily:

var appleCount = 0; function addApple() { appleCount = appleCount + 1; } function howManyApples() { return appleCount; } addApple(); alert(howManyApples()); 

Better example - only creates one global variable:

var appleCounter = { count: 0, add: function() { this.count = this.count + 1; }, howMany: function() { return this.count; } }; appleCounter.add(); alert(appleCounter.howMany()); 

Best example - creates no global variables:

(function(){ var appleCounter = { count: 0, add: function() { this.count = this.count + 1; }, howMany: function() { return this.count; } }; appleCounter.add(); alert(appleCounter.howMany()); })(); 

Global variables should be avoided in reusable scripts.

If you're writing simple functions that will only be used in one page, there's nothing wrong with using globals.

If you're writing a reusable component or a complex web page, you should use closures or namespaces instead.

For more specific advice, please provide more detail.

EDIT: You should create an XmlData class.

For example:

function XmlData(...) { this.data = ...; } XmlData.prototype.doSomething = function(...) { //Use this.data } 

Depending on how what your data comes from, you may want to make a separate function to retrieve the data.

Here is a good explanation.

Create a namespace, put all your functions within that namespace.

MyNS = { x: 1, y: 2 // Here you define shared variables }; MyNS.func1 = function(){}; // Here you define your functions that need those variables 

Avoid global variables, it's bad programming. Try pass it as an argument or use name spacing to restrict its scope.