Statements
Javascript the Definitive Guide by David Flanagan

CpSc 217 - Structured and Dynamic Web Programming

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This chapter is a partial Review from 130

Basics

Equality and Relational Operators

  • = = != //be careful with = =
  • < > <= >=
  • Boolean expressions: not, and, or ! && ||
  • Precedence revisited
Conditional Programming
  • Not sequential
  • When needed to choose between two (or more) alternatives
  • IF syntax for single statements

    • if ( condition )
       statement;
  • examples of Javascript code

    • if ( input_num < 0 )
          document.write ( "Error message<br>");
  • IF syntax for multiple statements

    • if ( condition )
    {
               statement1;
               statement2;
    }
  • examples of Javascript code

    • if ( grade == 100 )
    {
              document.write( "Excellent job<br>");
              bonus = 1;
    }

IF-ELSE syntax

  • single statements

    • if ( condition )
         statement;
    else
         statement;
  • examples of Javascript code

    • if (x < 0 )
         document.write( "negative number<br>");
    else
         document.write( "non-negative number<br>");
  • Nested IFs
    • More than two possible actions
    • Second if can be nested inside of the 1st "if" part or the 1st "else" part
    • Examples

    if ( x <0 )
         document.write( "negative number<br>");
    else
         if ( x == 0 )
         document.write( "zero<br>");
    else
              document.write( "positive number<br>");
     
ELSE IFs

    if (x < 0 )
         document.write( "negative number<br>");
    else if (x == 0)
         document.write( "zero<br>");
    else
         document.write(" "positive number<br>");
Multi-way selection: The Switch statement
  • Used in place of if-elseif-elseifÂ…
  • Syntax

    • switch ( variable)
    {
         case1:     statements;
              break;
         case2:     statements;
              break;
         . . .
         casen:     statements;
              break;
         default:     statements;
    }

Loops

  • while, for, do
  • Increment/Decrement revisited
    • I = I + 1
    • I += 1
    • I++
    • ++I

WHILE Loops
  • Syntax

    • while (condition)
    {
         statements_in_the_loop;
    }
    initialize; while (test) {    statement    increment }
  • Semantics
    1. Evaluate the condition
    2. If the condition is true

      3. Execute the statements in the loop
      Jump back to the top of the loop (step 1.)
    3. Otherwise
           Execute statements after the loop

int sum = 0, i = 1;
while (i < 10)
{
     sum = sum + i;
     i++;
}
FOR loop & Counter Controlled loops
  • Syntax for initial, final, and modifier

    • for (initialize_lcv; condition; modify_lcv)
    {
         statements_in_loop;
    }
    statements_after_loop
  • Semantics
    1. Initialize lcv
    2. Evaluate the condition
      1. If the condition is true

        2. Execute the statements in the loop
        Jump back to the top of the loop (step 1.)
      2. Otherwise
             Execute statements after the loop
  • EXAMPLES

    • for (I=0; I<9; I++)
         document.write( I);
     
  • Also a for in loop
    Used with arrays and objects

    for (variable in object)
       statement

Break

  • Used to exit loop
  • Caution when using
  • Not "structured"
  • Sometimes appropriate


Continue

  • Used to skip to next iteration of loop
  • Caution when using
  • Not "structured"
  • Rarely appropriate