JavaScript For Loop Tutorial

JavaScript Loops

Loops can execute a block of code a number of times. if you want to run the same code over and over again, each time with a different value.

Instead of writing:

text += bikes[0] + “<br>”; 
text += bikes[1] + “<br>”; 
text += bikes[2] + “<br>”;
text += bikes[3] + “<br>”;
text += bikes[4] + “<br>”;
text += bikes[5] + “<br>”;

You can write:

for (i = 0; i     text +=bikes[i] + “
“;
}

JavaScript supports different kinds of loops:

• for 
• for/in 
• while 
• do/while 

The For Loop In JavaScript

The for loop is often the tool you will use when you want to create a loop.

Syntax: for(initializer; condition; iteration) { // Code to be executed }

The for loop requires the following three parts.

• Initializer: Initialize a counter variable to start with
• Condition: specify a condition that must be evaluated to be true for the next iteration
• Iteration: increase or decrease the counter

The For/In Loop In JavaScript

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

Example

var person = {fname:”John”, lname:”Doe”, age:25}; 

var text = “”;
var x;
for (x in person) {
    text += person[x];
}