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for…in loop

Updated on Sep 3, 2025
 
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The JavaScript for…in loop is used to iterate over properties of Objects. In JavaScript, Arrays are also Objects and each character in a string have an index. So, we can use them also to iterate over Arrays and Strings.

//Object example
const obj = {
a: 1,
b: 2,
c: 3,
d: 4
}
for (const key in obj) {
console.log( obj[key] )
}

// Output:

1 2 3 4
//Array example
const array = ['a', 'b', 'c', 'd'];
for (const index in array) {
console.log(array[index])
}

// Output:

a b c d
//String example
const string = 'Web Developer';
for (const index in string) {
   console.log(string[index])
}

//Output:

W e b D e v e l o p e r
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