Why the first 'foo' is showing undefined as output? Would u pls help me to solve out the beneath problem?

Question

var i = 0;
var a = {
['foo' + i++]: i,
['foo' + ++i]: i,
['foo' + ++i]: i
};

console.log(a.foo1); // 1
console.log(a.foo2); // 2
console.log(a.foo3); // 3

Answer 1

Put this line after definition for <a>

console.log( JSON.stringify( a ) )

You'll see that <a> doesn't have any member named 'foo1'.

(Edit)
In case you're wondering, why it has 'foo0', 'foo2' and 'foo3' members, but not 'foo1' - then know that the difference was due to the use of post and pre increment operator, which modifies value of <i> in different manner.