JavaScript Basics

JavaScript Data Types

• Primitive Data Types:
  • Numbers: e.g., 123, 120.50
  • Strings: e.g., "This text string"
  • Boolean: e.g., true or false
• Trivial Data Types:
  • null
  • undefined
• Composite Data Type:
  • Object (to be covered in detail later)

JavaScript Variables

• Variables: Named containers for data.
• Declaration: Must use the var keyword.
  • e.g., var money; or var money, name;
• Initialization: Storing a value in a variable.
  • Can occur at creation or later.
  • Example: var name = "Ali";, money = 2000.50;
• Scope:
  • Global Variables: Accessible anywhere in the code.
  • Local Variables: Accessible only within the function it's defined.

Variable Scope in JavaScript

• Local vs Global:
  • A local variable can have the same name as a global variable, but it hides the global one.
  • Example:
    javascript var myVar = "global"; function checkscope() { var myVar = "local"; document.write(myVar); }

Naming Conventions

• Do not use reserved keywords (e.g., break, boolean).
• Names must start with a letter or underscore, not a numeral.
  • Valid: _123test | Invalid: 123test
• Variable names are case-sensitive (e.g., Name vs name).

Reserved Words in JavaScript

• Reserved words cannot be used as variable names:
  • abstract, boolean, break, byte, case, catch, char, class, const, continue, debugger, default, delete, do, double, else, enum, export, extends, false, final, finally, float, for, function, goto, if, implements, import, instanceof, int, interface, long, native, new, null, package, private, protected, public, return, short, static, super, switch, synchronized, this, throw, throws, transient, true, try, typeof, var, void, volatile, while, with.