In JavaScript, I am looking into looping, and there are certain ways to loop. Of course there are basic things as for loop, while loop, do while loop, .. but there are two new (to me..) loops, which are for in loop, and for out loop.

The description of for-in loop : “This loop iterates (in an arbitrary order) over the name of each enumerable property in an object, allowing statements to be executed for each distinct property.”


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

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

and description of for-of loop : “This loop iterates over iterable objects such as an Array, Map, Set, String, TypedArray, arguments object, etc.


const iterable = ['mini', 'mani', 'mo'];

for (const value of iterable) {
  console.log(value);
}

It essentially iterates over the value of each distinct property in the structure, such as each letter in a word or each element in an array.

Also for arrays, you could also use foreach, which is embedded in array’s prototype so we can only use it to an array.

We can also can get the indexes in foreach also.


arr.forEach(function(element, i) {
  console.log('Element', i, 'is', element);
});

This is a good post for this topic https://medium.com/@abustamam/for-loops-vs-foreach-in-javascript-7a977278a39e

Some other things to note about foreach loops is that it is about 95% slower than for loop, so just use for loops.. and that it is calling a callback function for every elements in javascript arrays so it is not valid for cases when you want to return outside the loop!!