JavaScript Topics

• Where to put JavaScript Code
  1. Inside the <script> element  
  2. The "onclick" attribute of the <button> element   

   

• Variables
  • Declarations  (var x;)
  • Initialization  ( x = 15; )

   

• Statements
  • Assignment  (  x = x + 1; )
  • Statement terminator (;)
  • Grouping statements in statement blocks
    • Use curly braces:  {}
• Comments  (two types)
  1. //  The double slash is for a single line comment. 

     //  This means that the JavaScript interpreter ignores

     //  everything after the double slash but only to the

     //  end of the current line.

      

     • Example:   age = 7 * age;   // Converts dog years to human years.

      

  2. /*  This comment can proceed across multiple lines of the source code.  Everything between the delimiters is ignored by the JavaScript interpreter. */

     

• Functions
  • How to call built-in functions  (  Math.round(3.4);  )
  • How to define your own.      (   function printThis(s)  {document.write(s);}  )
  • How to call your own.   (   printThis("You have arrived on Planet Jeff!");  )

   

• Random Numbers
  • Math.random()
  • Multiplicative scaling:   
    • Math.random()*100 ; //  Gets you a random (floating pt.) number between 0 and 99 inclusive
  • Converting from floating point numbers to integers:
    • Math.round( 100 * Math.random() );  // Gets you a random INTEGER between 0 and 99 inclusive.
  • Shifting the range:  
    • Math.round( 100 * Math.random() ) + 1 ;  //  Gets you a random INTEGER beteen 1 and 100, inclusive.

     

• Conditional Execution  (if-then-else)
  • if-then   versus  if-then-else

   

• Scoping  (the SCOPE of variables)