JavaScript: Object variable changes [duplicate]

Question

var y = {a:200,b:{}}; 
console.log(y); 
y.a = 100; 
y.b[1] = 10; 
y.b[2] = 20; 
console.log(y); 

Both the results on the console are same. Any idea why?

Result for line 2 
Object {a: 200, b: Object} a: 100 b: Object 1: 10 2: 20 
Result for Line 6 
Object {a: 100, b: Object} a: 100 b: Object 1: 10 2: 20

Answer 1

console.log() has some funny behaviors in some browsers (I've seen it in Chrome) that probably has to do with the fact that console itself is in a different process and data has to get marshalled across a process boundary in the background (so it isn't done synchronously with your Javascript execution).

It appears that when you do something like console.log(y); and y is an object, what is immediately stored for the console is a reference to y and then sometime slightly later, the actual contents of y are fetched and displayed. But, if in the meantime your Javascript has modified y, then you won't necessarily get the exact right value for y displayed in the console.

You can work-around this issue by doing this:

console.log(JSON.stringify(y)); 

And, in fact you can test your code by changing both of your console.log() statements to this.