JavaScript for in loop

In JavaScript, for...in loop is similar to for loop to iterate over an objects or array elements. The loop allows you to perform an action on each property of an object or element of an array.

Syntax of the Javascript For In Loop

for(var property in object)  
{  
    // code to be executed  
}

Here, property is a string variable representing the property key, and object is the object to be iterated over.

Iterating Over an Object Example

const numbers = {
    "one": 1,
    "two": 2,
    "three": 3,
    "four": 4,
    "five": 5
}

for (let num in numbers) {
  console.log(`${num}: ${numbers[num]}`);
}

Output:

one: 1
two: 2
three: 3
four: 4
five: 5

Iterating Over an Array Example

const numbers = [1, 2, 3, 4, 5]; 
for (let index in numbers) {
    console.log(`Index: ${index} Value: ${numbers[index]}`); 
}

Output:

Index: 0 Value: 1
Index: 1 Value: 2
Index: 2 Value: 3
Index: 3 Value: 4
Index: 4 Value: 5

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