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JavaScript | While Loop
  • Last Updated : 06 Mar, 2019
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While Loop: A while loop is a control flow statement that allows code to be executed repeatedly based on the given Boolean condition. The while loop can be thought of as a repeating if statement.

Syntax:

while (condition) {
    // Statements
}

Example: This example illustrates the use of while loop.




<!DOCTYPE html>
<html>
  
<head
    <title>
        JavaScript While loop
    </title>
</head
  
<body style="text-align:center;">
  
    <div>
        <h1>GeeksForGeeks</h1>
          
        <h2>JavaScript While Loop</h2>
    </div>
      
    <p id="GFG"></p>
      
    <!-- Script to use while loop -->
    <script>
        var print = "";
        var val = 1;
          
        while (val < 6) {
            print += "Geeks " + val;
            print+="<br>"
            val+=1;
        }
          
        document.getElementById("GFG").innerHTML
                = print;
    </script>
</body>
  
</html>                    

Output:

Do-While loop: A do-while loop is a control flow statement that executes a block of code at least once, and then repeatedly executes the block or not depending on a given boolean condition at the end of the block.



Syntax:

do {
    // Statements
}
while (condition);

Example: This example illustrates the use of do-while loop.




<!DOCTYPE html>
<html>
  
<head
    <title>
        JavaScript While loop
    </title>
</head
  
<body style="text-align:center;">
  
    <div>
        <h1>GeeksForGeeks</h1>
        <h2>JavaScript While Loop</h2>
    </div>
      
    <p id="GFG"></p>
      
    <!-- Script to use do-while loop -->
    <script>
        var print = ""
        var val = 0;
  
        do {
            print += "Geeks " + val;
            print +="<br>";
            val+=1;
        }
        while (val < 6); 
  
        document.getElementById("GFG").innerHTML
                = print;
    </script>
</body>
  
</html>                    

Output:

Comparison between while and do-while loop: The do-while loop executes the content of the loop once before checking the condition of the while loop. While the while loop will check the condition first before executing the content.

While LoopDo-While Loop
It is an entry condition looping structure.It is an exit condition looping structure.
The number of iterations depends on the condition mentioned in the while block.Irrespective of the condition mentioned in the do-while block, there will a minimum of 1 iteration.
The block control condition is available at the starting point of the loop.The block control condition is available at the end point of the loop.

Example: This example illustrates both while and do-while loop.




<!DOCTYPE html>
<html>
  
<head
    <title>
        JavaScript loop
    </title>
</head
  
<body style="text-align:center;">
  
    <div>
        <h1 style="color:green;">
            GeeksForGeeks
        </h1>
          
        <h2>JavaScript Loop</h2>
    </div>
      
    <h3>While Loop</h3>
      
    <p id="GFG"></p>
      
    <!-- Script to use while loop -->
    <script>
        var text = "";
        var i = 1;
        while (i < 6) {
            text += "Geeks " + i+"<br>";
            i++;
        }
          
        document.getElementById("GFG").innerHTML
                = text;
    </script>
      
    <h3>Do While Loop</h3>
      
    <p id="GFG1"></p>
      
    <!-- Script to use do-while loop -->
    <script>
        var text = ""
        var i = 1;
      
        do {
            text += "Geeks " + i+"<br>";
            i++;
        }
        while (i < 6); 
      
        document.getElementById("GFG1").innerHTML
                = text;
    </script>
</body>
  
</html>                    

Output:

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