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.