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For Loop in JavaScript

By Priya PedamkarPriya Pedamkar

Home » Software Development » Software Development Tutorials » JavaScript Tutorial » For Loop in JavaScript

For Loop in JavaScript

Introduction to For Loop in JavaScript

The For Loop in JavaScript is the best method to iterate through a series of data at the same time. For loop is an entry-controlled loop in which the test condition checked before going to the body of the program. For loop is used when we know the number of iterations before entering the loop. Loops are usually used for repeating a series of steps a certain number of times, so they often involve counter variables, a conditional test, a way of changing the counter variable. In many cases For loop can achieve the same thing as a while loop, with fewer lines of code.

Types of For Loop in JavaScript

  • For: It is used to loop through code n number of times till the condition is false
  • For/in: It is used to loop through object properties
  • For/of: It is used to loop through an array of iterable objects

For loop Syntax

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for (Initialization condition; test condition; Increment/Decrement)
{
Body of loop
}

For/in loop Syntax

for (var in object)
{
Body of loop
}

For/of loop Syntax

for (variable of iterable)
{
Body of loop
}

The Workflow of For Loop in JavaScript

  1. Initialization Condition: The condition states the start of the for loop. The variable can be initialized at a loop or variable can be declared separately.
  2. Testing Condition: For loop is an Entry Control Loop, the condition is checked before the program executes. It also tests the exit condition of the loop.
  3. Statement Execution: Only if the test condition is true, then the body of the loop is executed.
  4. Increment/ Decrement: For every cycle, after the loop executes, the control goes to increment statement. Here it Increment or decrement the control variables.
  5. Loop Termination: The loop terminates as soon as the condition becomes false.
Note: We can skip the initialization condition inside the For loop if we want, but ( ; ) Semicolon should not be removed. If it is removed, then the program will throw an error. The variable can be declared outside the loop.

Example

Int add=10;
For(;add<30;add++)

How For Loop Works in JavaScript?

When loop executes, the initial condition checked. This is the initial value where the loop starts. Next step, the condition tested whether the provided condition is true or false; this determines whether the loop should continue or not. If the condition is true, then the variable modifies the loop, and the loop statement executes. After the Statement executes, the loop restarts until the condition is false.

Flow chart of For Loop

Below is the Flow Chart of For Loop in JavaScript:

 Flow chart

The loop executes first and for loop checks the test condition, whether it is true or not. If the condition is true, then it will go to the statement block where the program is executed. If the condition is false, then the loop will exit, and the program will be stopped.

Example #1: Using For Loop

The below program is written to print the list of student names using JavaScript.

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Code:

<html>
<head>
<script type="text/JavaScript">
var students = new Array("John", "Ann", "Aaron", "Edwin", "Elizabeth");
document.write("<b>Using for loops </b><br />");
for (i=0;i<students.length;i++)
{
document.write(students[i] + "<br />");
}
</script>
</head>
<body>
</body>
</html>

Output:

list of student names

Example #2: Using For Loop

Code:

<html>
<body>
<script>
for (var iterator1 = 0; iterator1 < 5; iterator1++) //initialization, condition, increment
{
document.write(iterator1 + 1 + ". " + "For loop Tutorial for JavaScript</br>");
}
document.write("</br>Loop end");
</script>
</body>
</html><>

Output:

For Loop in JavaScript

Note: For loop ends after 5 iterations.

Example #3: Using For/in Loop

The for/in loop is used for iterating through the properties of an object.

Code:

<html>
<body>
<script type="text/JavaScript">
var string1 = "";
var object1 = {a: 1, b: 2, c: 3};
for (var property1 in object1)
{
string1 += object1[property1];
}
document.write(string1);
</script>
</body>
</html>

Output:

Using For/in Loop

Example #4: Using For/of Loop

Code:

<html>
<body>
<h2>JavaScript For/Of Loop</h2>
<p>The for/of statement loops through the values of an iterable object.</p>
<script>
var cars = ['BMW', 'Volvo', 'Mini'];
var x;
for (x of cars) {
document.write(x + "<br >");
}
</script>
</body>
</html>

Output:

Using For/of Loop

Conclusion

At first, for loop might look a little confusing, but once you figure out the different parts of the for statement, they aren’t hard. Just keep in mind that each for loop begins with the keyword for, followed by a set of parentheses containing three parts, a pair of curly braces. For loop helps programmer to write a program in an effectively and easily. It saves the problem of writing multiple lines of code consuming more time. For a programmer to write a program effectively and productively. The Forgives an added advantage as it reduces the length of the program.

Recommended Articles

This has been a guide to For Loop in JavaScript. Here we discuss Introduction to For Loop in JavaScript and its Types along with Flowchart. You can also go through our other suggested articles to learn more –
  1. For Loop in Python
  2. For Loop in Java
  3. Iterator in Java
  4. For Loop in Matlab

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