Javascript - Statement for Statement

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Introduction

The for statement is a pretest loop.

for loop has the capabilities of variable initialization before entering the loop.

It also defines postloop code. Here's the syntax: 

for (initialization; expression; post-loop-expression)
   statement

And here's an example: 

var count = 10;
for (var i=0; i < count; i++){
    console.log(i);
}

This code defines a variable i that begins with the value 0.

The for loop is entered only if the conditional expression (i < count) evaluates to true.

If the body is executed, the postloop expression is also executed, iterating the variable i.

This for loop is the same as the following while loop: 

var count = 10;
var i = 0;
while (i < count){
    console.log(i);
    i++;
}

The for loop encapsulates the loop-related code into a single location.

The loop controlling variable i can be defined outside the initialization: 

var count = 10;
var i;
for (i=0; i < count; i++){
    console.log(i);
}

The variable i defined inside the loop is accessible outside the loop as well. For example: 

var count = 10;
for (var i=0; i < count; i++){
    console.log(i);
}
console.log(i);    //10

In this example, it displays the final value of the variable i after the loop has completed.

The initialization, control expression, and postloop expression are all optional.

You can create an infinite loop by omitting all three, like this: 

for (;;) {              //infinite loop
   doSomething();
}

Including only the control expression turns a for loop into a while loop: 

var count = 10;
var i = 0;
for (; i < count; ){
    console.log(i);
    i++;
}