JavaScript For in Loop

 

The For In Loop

The JavaScript for in statement loops through the properties of an Object:

for (key in object) {
  // code block to be executed
}

Example

const person = {fname:"John", lname:"Doe", age:25};

let text = "";
for (let x in person) {
  text += person[x];
}

Example Explained

• The for in loop iterates over a person object
• Each iteration returns a key (x)
• The key is used to access the value of the key
• The value of the key is person[x]                 

  For In Over Arrays

  The JavaScript for in statement can also loop over the properties of an Array: for (variable in array) {
    code
  }

  Example

  
  

• const numbers = [45, 4, 9, 16, 25];

  for (let x in numbers) {
    txt += numbers[x];
  }

• let txt = "";