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eavnitech
eavnitech

Posted on • Updated on • Originally published at eavnitech.com

Loop and iteration in javascript with example

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

[].map(callback);

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Example

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.

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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


[].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


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Example

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

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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.

for( initialization; condition; increment/decrement){

    // Your logic
}

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Example

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

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  • 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.


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

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Example

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
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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.

do {
  // Your logic
}
while (condition);

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Example


let result = '';
let i = 0;

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

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

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6. for in

This is used to iterate the properties of the object.


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

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  • 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


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

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

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

// output
10
20
30
40
50


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

Thank you :)

I will be happy to answer your queries on my Twitter handle Twitter

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