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JS: for loop | JavaScript

JavaScript for loop

The for loop iterates the block of statments, expecting three optional statements seperated by semicolon (;)

Syntax

for(intialization(s); condition(s); increment(s)){ //body } for(var i = 0; i < 10; i++){ //body }

All the three arguments are the JavaScript valid statements;

initialization var i = 0

new variable(s) can be intialized as well as reassign a value, seperated by comma.

condition i

for loop checks the condition for each iteration. One or more conditions can be given. All condition must be true.

increment i++

one or more variables values can be changed, increment or decrement allowed.

Terminate for-loop

A for loop can be terminated with break keyword.

for(i = 1; i <= 100 ;i++) if(i > 10) break; else console.log(5, 'x', i, '=', 5 * i); 5 x 1 = 5 5 x 2 = 10 5 x 3 = 15 5 x 4 = 20 5 x 5 = 25 5 x 6 = 30 5 x 7 = 35 5 x 8 = 40 5 x 9 = 45 5 x 10 = 50

The program prints table of 5, from 1 through 10. At 11th iteration, loop will be terminated with break keyword to exit the loop.

Jump to next iteration

A for loop may call its next iteration in the loop-block using continue keyword:

Following program prints even numbers only.

for(i = 1; i <= 10 ;i++) if(i % 2 == 1) //i.e. odd number continue; //next iteration else console.log(i); //print the even number 2 4 6 6 8 10

for in and for of Differenece

consider an array of fruits

var arr = ['Apple', 'Banana', 'Cherry'];

Following are two diffrent output

for(var o in arr) console.log(o); 0 1 2 for(var o of arr) console.log(o); Apple Banana Cherry

for of

for-of works with iterable variables and expressions only. for-of iterates the elements of an array.

for in

for-in iterates the properties of an object and index of an array.

  1. JavaScript for-loop consists of three parts seperated by semicolon.
  2. All three parts are optional
  3. for-of requires iterable types only
  4. for-of iterates the elements of the given array
  5. for-in iterates the 0-based index of the given array
  6. for-in iterates the properties of the given object

falsy expressions do while