Chapter 3: Debugging for Dummies

Variable Scope Syndrome: The Most Commonly Misdiagnosed Disease of Modern Programming

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Variable Scope Syndrome is a condition where a programmer is unable to tell where a variable is declared, used, or modified. Symptoms include:

• Confusion about variable accessibility across functions
• Difficulty in understanding variable persistence between scopes
• Unexplained changes to global variables

The most common cause of Variable Scope Syndrome is poor naming conventions and lack of documentation.

Here's an example of the disease in action:

			var myVar = 10;
			function doSomething() {
				var myVar = 20;
				return myVar;
			}
			console.log(myVar); // outputs 10, but should output 20
		

To cure Variable Scope Syndrome, use block-level scope with let or const instead of var.

Learn how to split your code with block-level scope.