Type casting when == used instead of === [duplicate]

Question

I generally don't prefer using == but today i was just experimenting with the following code including == and the results are a bit confusing to me. Can someone please explain what is happening?

All these are falsy values:

'', 0, false, undefined, null

Suppose i did:

if (undefined == null) {
    alert('a');
} else {
    alert('b');
}

The statements below give true:

null == undefined
0 == ''
false == ''
0 == false

But why does the code below return false?

undefined == 0
undefined == ''
null == 0

Answer 1

Because 0, false and '' are "values" while null is "absence of value" and undefined is "absence of definition".

Thus, you can compare "values" with each other, same for "non-values". But you can't compare "values" with "non-values".