Loop 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 function in JavaScript with example

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);

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.

2. forEach loop in JavaScript with example

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

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

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

3. for loop in JavaScript with example

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

for( initialization; condition; increment/decrement){

    // Your logic
}

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

• 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 loop in JavaScript with example

while loop executes the logic(code) once the condition is true.

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

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

5. Do while loop in JavaScript with example

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);

Example

let result = '';
let i = 0;

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

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

6. for in loop in JavaScript with example

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

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

7. for of loop in JavaScript with example

for of is used to iterate the array of object.

Syntax

for (variable of iterable) {
  // statement
}

Example

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

Conclusion

We have learnt different type of loop and function to iterate the JavaScript Arrray and Object.

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