JavaScript Loop For

JavaScript Tutorial � JavaScript Loop For

Loops can execute a block of code a number of times.

Loop instructions are used to execute a code sequence in mode repeatedly.
In JS there are two different types of repetitive instructions:

1. for - repeats a sequence of code a specified number of times
2. while - repeats a sequence of code as long as a condition is true Array:

Example:

<!DOCTYPE html>
<html>
<body>

<h2>JavaScript For Loop</h2>

</body>
</html>

output:
Ford
Audi
Skoda
Opel
Fiat
Renault
Toyota

For Loop - example

The for statement is used when the desired number of iterations for the code sequence is known in advance.

for loop has the following syntax::

for�(statement 1;�statement 2;�statement 3) {
��//�code block to be executed
}

Statement 1 is executed (one time) before the execution of the code block.
Statement 2 defines the condition for executing the code block.
Statement 3 is executed (every time) after the code block has been executed.

Example:

      <!DOCTYPE html>

        <html>

        <body>
      <h2>JavaScript For Loop</h2>
      <p id="demo1"></p>
      <script>

        var my_text = "";

        var i;

        for (i = 0; i < 6; i++) {

        my_text += "My number is " + i + "<br />";

        }

        document.getElementById("demo1").innerHTML = my_text;

  </script>
     </body>

        </html>

first instruction sets a variable before the loop starts (var i = 0).

second instruction defines the condition for the loop to run (i must be less than 6).

the third instruction increases a value (i++) each time the code block in the loop has been executed.

For/In Loop - example

JavaScript for/in statement loops through the properties of an object:

Example: syntax

examples of arrays

Example:

<!DOCTYPE html>

  <html>

  <body>
<h2>JS For/In Loop</h2>
<p>for/in loops through the properties of an object.</p>
<p id="my_demo"></p>
<script>

  var my_txt = "";

  var my_person = {fname:"Johny", lname:"Dared", age:31}; 

  var x;

  for (x in my_person) {

  my_txt += my_person[x] + " ";

  }

  document.getElementById("my_demo").innerHTML = my_txt;

  </script>
</body>

  </html>

Output:

JavaScript For/In Loop

The for/in statement loops through the properties of an object.
Johny Dared 31

For/Of Loop, example

for/of lets you loop over data structures that are iterable such as Arrays, Strings, Maps, NodeLists, and more.

for/of loop syntax::

for�(variable�of�iterable) {
��//�code block to be executed
}

Looping over an Array

Example:

<!DOCTYPE html>

  <html>

  <body>
<h2>JavaScript For/Of Loop</h2>
<p>The for/of statement loops through the values of an iterable object.</p>
<script>

  var my_cars = ["Ford", "Audi", "Skoda", "Opel", "Fiat", "Renault", "Toyota"];

  var x;
for (x of my_cars) {

  document.write(x + "<br >");

  }

  </script>
</body>

  </html>

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JavaScript Loop For - javascript tutorial

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