Vfrdtyky

I may be asking a basic question but I don't know how to clear such a confusion through google search

this below code works fine and count words, so I was trying to understand further

var words = chunk.trim().split(' ');

       var counts = {};



   // Count words

   words.forEach(function (word) {

       word = word.trim();



       if (word.length) {

           if (!counts[word]) {

               counts[word] = 0;

           }



           counts[word]++;

       }

   });

then why not this below gives me 1,2 . I am expecting 1,2 and its giving me 2,2

var a = function(){

  var a, b;

  var  obj = {}

   obj[a]=1;

   obj[b]=2;



  console.log(obj[a]);

  console.log(obj[b]);

}



var res = a();

Why doesn't this give me 1,2? I am expecting 1,2 and it's giving me 2,2

This is happening because a == b; they are both undefined because you never assigned them values on the line var a, b. When you omit the = assignment in var declarations, the default value of undefined is used instead, meaning that your line becomes var a = undefined, b = undefined.

Thus, the second property assignment (obj[b] = 2) is actually overwriting the first (obj[a] = 1). Your obj only contains a single key, and after running your code its overall structure looks like:

{

  'undefined': 2

}

var a = function () {

  var a, b

  var obj = {}

  obj[a] = 1

  obj[b] = 2



  console.log(obj)

}



var res = a()

If you want the results you expected, you need to use distinct keys, like the strings 'a' and 'b':

var a = function() {

  var a = 'a', b = 'b'

  var obj = {}

  obj[a] = 1

  obj[b] = 2

  

  console.log(obj)

  console.log(obj[a], obj[b])

}



var res = a()

Because you're only declaring (not assigning) both a and b, and in javascript a not assigned variable is implicitely undefined.

you're essentially referring to obj[undefined] twice

var a,b; //here both the variables are undefined



obj[a]=1; 

obj[b]=2; //you're overriding the variable





console.log(obj[a]); //2

console.log(obj[b]); //2

When you say obj[a], javascript tries to create a property on obj with the value in a. Since value in a is undefined, the string representation is "undefined" and hence a property undefined is created on obj.
Since b also happens to have undefined value, you are essentially writing 2 onto the same property undefined.

Hence you get 2 both the times.
Actually if you log obj and see the value in console, you would see:

Object {undefined: 2}

undefined:2