MyTetra Share
Делитесь знаниями!
Loop ... controls - using labels
Время создания: 13.05.2017 23:43
Раздел: javaScript - Statements
Запись: xintrea/mytetra_db_mcold/master/base/1494708207q480zpx8h2/text.html на raw.githubusercontent.com 
<html>
   <body>
      
      <script type="text/javascript">
         <!--
         var x = 1;
         document.write("Entering the loop<br /> ");
         
         while (x < 20)
         {
            if (x == 5){
               break; // breaks out of loop completely
            }
            x = x + 1;
            document.write( x + "<br />");
         }
         
         document.write("Exiting the loop!<br /> ");
         //-->
      </script>
      
      <p>Set the variable to different value and then try...</p>
   </body>
</html>

Output

Entering the loop
2
3
4
5
Exiting the loop!
Set the variable to different value and then try...

We already have seen the usage of break statement inside a switch statement.

The continue Statement

The continue statement tells the interpreter to immediately start the next iteration of the loop and skip the remaining code block. When a continue statement is encountered, the program flow moves to the loop check expression immediately and if the condition remains true, then it starts the next iteration, otherwise the control comes out of the loop.

Example

This example illustrates the use of a continue statement with a while loop. Notice how the continue statement is used to skip printing when the index held in variable x reaches 5 −

<html>
   <body>
      
      <script type="text/javascript">
         <!--
            var x = 1;
            document.write("Entering the loop<br /> ");
         
            while (x < 10)
            {
               x = x + 1;
               
               if (x == 5){
                  continue; // skip rest of the loop body
               }
               document.write( x + "<br />");
            }
         
            document.write("Exiting the loop!<br /> ");
         //-->
      </script>
      
      <p>Set the variable to different value and then try...</p>
   </body>
</html>

Output

Entering the loop
2
3
4
6
7
8
9
10
Exiting the loop!

Using Labels to Control the Flow

Starting from JavaScript 1.2, a label can be used with break and continue to control the flow more precisely. A label is simply an identifier followed by a colon (:) that is applied to a statement or a block of code. We will see two different examples to understand how to use labels with break and continue.

Note − Line breaks are not allowed between the ‘continue’ or ‘break’ statement and its label name. Also, there should not be any other statement in between a label name and associated loop.

Try the following two examples for a better understanding of Labels.

Example 1

The following example shows how to implement Label with a break statement.

<html>
   <body>
      
      <script type="text/javascript">
         <!--
            document.write("Entering the loop!<br /> ");
            outerloop: // This is the label name
         
            for (var i = 0; i < 5; i++)
            {
               document.write("Outerloop: " + i + "<br />");
               innerloop:
               for (var j = 0; j < 5; j++)
               {
                  if (j > 3 ) break ; // Quit the innermost loop
                  if (i == 2) break innerloop; // Do the same thing
                  if (i == 4) break outerloop; // Quit the outer loop
                  document.write("Innerloop: " + j + " <br />");
               }
            }
         
            document.write("Exiting the loop!<br /> ");
         //-->
      </script>
      
   </body>
</html>

Output

Entering the loop!
Outerloop: 0
Innerloop: 0 
Innerloop: 1 
Innerloop: 2 
Innerloop: 3 
Outerloop: 1
Innerloop: 0 
Innerloop: 1 
Innerloop: 2 
Innerloop: 3 
Outerloop: 2
Outerloop: 3
Innerloop: 0 
Innerloop: 1 
Innerloop: 2 
Innerloop: 3 
Outerloop: 4
Exiting the loop!

Example 2

<html>
   <body>
   
      <script type="text/javascript">
         <!--
         document.write("Entering the loop!<br /> ");
         outerloop: // This is the label name
         
         for (var i = 0; i < 3; i++)
         {
            document.write("Outerloop: " + i + "<br />");
            for (var j = 0; j < 5; j++)
            {
               if (j == 3){
                  continue outerloop;
               }
               document.write("Innerloop: " + j + "<br />");
            }
         }
         
         document.write("Exiting the loop!<br /> ");
         //-->
      </script>
      
   </body>
</html>

Output

Entering the loop!
Outerloop: 0
Innerloop: 0
Innerloop: 1
Innerloop: 2
Outerloop: 1
Innerloop: 0
Innerloop: 1
Innerloop: 2
Outerloop: 2
Innerloop: 0
Innerloop: 1
Innerloop: 2
Exiting the loop!
Так же в этом разделе:
 
MyTetra Share v.0.65
Яндекс индекс цитирования