how to know if a field exist inside an object? (as in javascript)

Question

And ofcourse I want to do this code-wise. It's not that there isn't alternative to this problem I'm facing, just currious.

Answer 1

if ('field' in obj) {
}

Answer 2

This will ignore attributes passed down through the prototype chain.

if(obj.hasOwnProperty('field'))
{
    // Do something
}