In nodeJs is there a way to loop through an array without using array size?

What you probably want is for...of, a relatively new construct built for the express purpose of enumerating the values of iterable objects:

let myArray = ["a","b","c","d"];
for (let item of myArray) {
  console.log(item);
}

... as distinct from for...in, which enumerates property names (presumably¹ numeric indices in the case of arrays). Your loop displayed unexpected results because you didn't use the property names to get the corresponding values via bracket notation... but you could have:

let myArray = ["a","b","c","d"];
for (let key in myArray) {
  let value =  myArray[key]; // get the value by key
  console.log("key: %o, value: %o", key, value);
}

_{¹Unfortunately, someone may have added enumerable properties to the array or its prototype chain which are not numeric indices... or they may have assigned an index leaving unassigned indices in the interim range. The issues are explained pretty well here. The main takeaway is that it's best to loop explicitly from 0 to array.length - 1 rather than using for...in.}

So, this is not (as I'd originally thought) an academic question, i.e.:

Without regard for practicality, is it possible to avoid length when iterating over an array?

According to your comment (emphasis mine):

[...] why do I need to calculate the size of an array whereas the interpreter can know it.

You have a misguided aversion to Array.length. It's not calculated on the fly; it's updated whenever the length of the array changes. You're not going to see performance gains by avoiding it (apart from caching the array length rather than accessing the property):

Now, even if you did get some marginal performance increase, I doubt it would be enough to justify the risk of dealing with the aforementioned issues.

To print 'item1' , 'item2', this code would work.

var myarray = ['hello', ' hello again'];

for (var item in myarray) {
    console.log(myarray[item])
}

You can use Array.forEach

var myArray = ['1','2',3,4]

myArray.forEach(function(value){
  console.log(value);
});