JavaScript provides full control to handle loops and switch
statements. There may be a situation when you need to come out of a loop
without reaching its bottom. There may also be a situation when you
want to skip a part of your code block and start the next iteration of
the loop.
To handle all such situations, JavaScript provides break and continue statements. These statements are used to immediately come out of any loop or to start the next iteration of any loop respectively.
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.
To handle all such situations, JavaScript provides break and continue statements. These statements are used to immediately come out of any loop or to start the next iteration of any loop respectively.
The break Statement
The break statement, which was briefly introduced with the switch statement, is used to exit a loop early, breaking out of the enclosing curly braces.Flow Chart
The flow chart of a break statement would look as follows −
Example
The following example illustrates the use of a break statement with a while loop. Notice how the loop breaks out early once x reaches 5 and reaches to document.write (..) statement just below to the closing curly brace −<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!
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