Loop and iteration in javascript with example
Tags: javascript, node
Published: 2021-03-24 18:11:51


Hello all, today we will learn the ways to iterate the array & object in the javascript.
Loop are the basic way to iterate the array & object.

### 1. Map
`map` is used to iterate the array elements & you can perform any operation on the element of the array like addition, subtraction, multiplication, division etc. 
it takes a callback function to iterate the array and return a new array.

Syntax
```javascript
[].map(callback);

```
Example
```javascript
let array = [10,20,30,40,50];


let returnValue = array.map((element) => element*10);

console.log(returnValue);

// output 
[ 100, 200, 300, 400, 500 ]

// in the map function we are multiplication 10 to every element.

```


### 2. forEach
`forEach` is used to iterate the array elements & it takes a callback function that will be called with each iteration of the array elements.

Syntax

```javascript

[].forEach(function(currentValue, index, arr), thisValue)

`currentValue` -> The value of the current element
`index` -> The array index of the current element
`arr` -> The array object the current element belongs to
`thisValue` -> A value to be passed to the function to be used as its "this" value.
If this parameter is empty, the value "undefined" will be passed as its "this" value


```
Example

```javascript
let array = [10,20,30,40,50];


array.forEach((value, index, arr) => console.log(value, index, arr));

// output

10 0 (5) [10, 20, 30, 40, 50]
20 1 (5) [10, 20, 30, 40, 50]
30 2 (5) [10, 20, 30, 40, 50]
40 3 (5) [10, 20, 30, 40, 50]
50 4 (5) [10, 20, 30, 40, 50]
undefined

```
The `undefined` is the returned value of the forEach() call.


### 3. for
`for` loop is the most basic and used loop in the programming language.

```javascript
for( initialization; condition; increment/decrement){

    // Your logic
}

```
Example

```javascript
let array = [10,20,30,40,50];
for(let i=0; i< array.length; i++){
    console.log(array[i]);
}

// output
10
20
30
40
50

```
- it is the fastest loop as compared to other loops
- it is an in-built loop and does not take any callback
- it is used to iterate the large size of the array
- We can use the `break` keyword to stop the iteration of the array


### 4. while 
`while` loop executes the logic(code) once the condition is true.
```javascript

// define any variable
while(condition){
    // your logic
    // increment/decrement the variable
}

```
Example

```javascript
let array = [10,20,30,40,50];
let index = 0;
while (index < array.length) {
    console.log(array[index]);
    index++;
}


// output

10
20
30
40
50
```

### 5. Do while
`do-while` loop executes the statement block atlease once the condition is false i.e. it will execute the statement once either the condition is false.
 
```javascript
do {
  // Your logic
}
while (condition);

```

Example

```javascript

let result = '';
let i = 0;

do {
  i = i + 1;
  result = result + i;
} while (i < 5);

console.log(result);
// Output : "12345"

```

### 6. for in
This is used to iterate the properties of the object.

```javascript

var array = { fname:"John", lname:"Doe", age:25 };

for(let element in array){
    console.log(element, array[element]);
}


// output

fname John
lname Doe
age 25

```
- Easy to use
- Syntax is very easy
- Does not have any callback


### 7. for of

`for of` is used to iterate the array of object.

Syntax
```javascript

for (variable of iterable) {
  // statement
}
```

Example

```javascript
let array = [10,20,30,40,50];

for(let element of array){
    console.log(element);
}

// output
10
20
30
40
50


```

- Easy to use
- Syntax is very easy
- Does not have any callback

Thank you :)

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