The for...in loop in JS

In: The left side is a string or can be converted to a string, the right is an object or an array

Example: Var person={firstname: "Bob", LastName: "Kin"};

for (x in person) {

Text = text + person[x];

}

document.write (text);//Output Bobkin

Using the for-in loop is also known as an "enumeration," which should be used on a non-array object's traversal. If used to loop an array, the array object has been enhanced by defined functions, logic errors can occur, and in for-in, the order of the list of attributes is not guaranteed. Therefore, the best array uses the normal for loop, and the object uses the For-in loop.

The for...in loop in JS