# Loops

If you want to print "Hello World!" 1000 times how will you do it? maybe you'll type console.log("Hello World!") 1000 times or maybe you'll copy-paste it. but in javascript, there is an easy way to do this, which is loops.

loops can execute blocks of code multiple times. Even if you want to execute a block each time with a different value.

There are 5 different types of loops in javascript:

### **for loop:**

The for statement creates a loop with 3 optional expressions.

**Syntax:**

```javascript
for (expression1; expression2; expression3){
//code to be executed 
}
```

**Example:**

```javascript
//this code print numbers from 1 to 10.
for (i=1; i<11 ; i++){
console.log(i)
}
```

**How for loop work? :**

In the above example, we have initialized a variable (i) in expression 1 whose value is going to change throughout the code.

Next, we gave a condition to our variable( i&lt;11 ) in expression 2 which will run the block of code if the condition is true.

Then in expression 3 we gave the increment operator to our variable which will increment the value until the condition(expression2) becomes false.

now let's see the behind-the-scenes of for loop by using **conditional** statements

```javascript
//behind the scenes of for loop 
let i=1 //expression1 in for loop

if (i<11) /*expression2 */  {
console.log(i) //block of code to be executed
i++ //expression3 
}

// Now you have to type this until the value of i becomes 11

// No need to read remaining code i just copy-pasted above code for 9 more times

 //No need to update variable again and again. increment operator will change the value of variable automatiaclly 

if (i<11) /*expression2 */  {
console.log(i) //block of code to be executed
i++ //expression3 
}

if (i<11) /*expression2 */  {
console.log(i) //block of code to be executed
i++ //expression3 
}

if (i<11) /*expression2 */  {
console.log(i) //block of code to be executed
i++ //expression3 
}

if (i<11) /*expression2 */  {
console.log(i) //block of code to be executed
i++ //expression3 
}

if (i<11) /*expression2 */  {
console.log(i) //block of code to be executed
i++ //expression3 
}

if (i<11) /*expression2 */  {
console.log(i) //block of code to be executed
i++ //expression3 
}

if (i<11) /*expression2 */  {
console.log(i) //block of code to be executed
i++ //expression3 
}

if (i<11) /*expression2 */  {
console.log(i) //block of code to be executed
i++ //expression3 
}

if (i<11) /*expression2 */  {
console.log(i) //block of code to be executed
i++ //expression3 
}
// above code will simply print the number from 1 to 10
```

It was a lot of code to type but **for** loops make it easy to read and work more efficiently.

### **for in loop:**

for in loops are the advanced version of for loops. they are used to run **for loop** for keys in an object.

**Syntax:**

```javascript
//let object ={some key-value pairs}

for (x in object) {
  code block to be executed
}
```

**Example:**

```javascript
let userInfo={
 username:"Virat Kohli",
 userage: 34
}

for (let a in userInfo){
   console.log(a) //this will only print keys in object & not values
}
```

for in loops also works for arrays.

### **for of loop:**

for of loops are used to run **for loop** for arrays and strings.

**Syntax:**

```javascript
for (x of iterable) {
  //block of to be executed
}
```

**Example:**

```javascript
for (let a of "Virat Kohli"){
console.log(a)
}
```

### **while loop:**

while loops are pretty much similar to for loop the only difference is the syntax.

**Syntax:**

```javascript
let expression1 // variable declaration 
while (expression2)/*condition for variable */ {
//block of code to be executed
expression3 // operator
}
```

if you don't give a valid operator to loop or if the condition for loop never becomes false then it will run the code infinitely causing the browser to crash.

**Example:**

```javascript
//this code print numbers from 1 to 10.
let i =1
while (i<11){
  console.log(i)
  i++
}
```

for loops and while loops are similar to each other so it doesn't matter which loop to use. It all depends on you, which loop you want to use.

### **do while loop:**

do-while loops are used to run a block of code once, no matter if the condition is true or false.

**Syntax:**

```javascript
do {
  //block of code to be executed
}
while (condition);
```

**Example:**

```javascript
let i=1 
do{
console.log(i)
i++
}
while(i<11)
```