Looping

• Looping means repeating a block of code while a condition is true.
• This is achieved in JavaScript using two statements, the while statement and the for statement.
  

The while Loop

• The while loop consists of a condition which, if it evaluates to true, causes the block of code inside the curly braces to execute once, and then the condition is re-evaluated.
• If it's still true, the code is executed again, the condition is re-evaluated again, and so on until the condition evaluates to false.
• var x = 0;
while (x < 10) {
   document.write(x);
   x++;
}
• TryIt Editor - while

while Loop syntax

• var x = 0;
while (x < 10) {
   document.write(x);
   x++;
}
• The initializer: var x = 0;
• The test condition: (x < 10);
• The increment: x++;
• Without an increment this would be an infinite loop.
  

The for Loop

• for (var x = 0; x < 10; x++)
{
   document.write(x);
}
• The initializer: var x = 0;
• The test condition:x < 10;
• The increment: x++
• ch3_examp4.htm
• TryIt Editor - for
  

The for...in Loop

• The for...in loop allows us to loop through each element in the array without having to know how many elements the array actually contains.
• In English
  "For each element in the array, execute some code."
• In JavaScript:
  for (index in arrayName) {
   //some code
}
• Example:
  var myArray = new Array("Paul","Paula","Pauline");
var elementIndex;
for (elementIndex in myArray){
   document.write(myArray[elementIndex]);
}
• TryIt Editor - for...in

The do...while loop

• The do...while loop is actually a while loop that excutes at least once.
• var x = 0;
do {
   document.write(x);
   x++;
} while (x < 10)
• TryIt Editor - do...while
  

The break and continue Statements

• Use the break statement to exit the loop prematurely
• TryIt Editor - break
• Use the continue statement to stop the execution of a loop, but instead of exiting the loop, start execution at the next iteration
• TryIt Editor - continue
  

Questions?