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);
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
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
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
breakkeyword 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
}
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
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
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
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
Thank you :)
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