1. What’s relationship between JavaScript and ECMAScript? 2. What does isNaN function do? 3. What is the function of Post Query? 4. What boolean operators does JavaScript support? - 5. How do you assign object properties?
Whether someone can or can't answer those questions during an interview will tell you very little about their skillset. I would ask to see code they have written.
I'd rather see if the candidate knew programming. Things like algorithms and data structures. Then, if he did, I'd ask him to write something in Javascript, some fairly complex function that I wrote a spec for. If he didn't know programming, of course, I wouldn't care how much he knew about Javascript, since he's not going to be able to develop any useful code.
The questions are fairly straightforward, but what benefit are they to an employer? It makes no sense to ask questions not related directly to programming in the language itself. These questions are not going to reveal a true understanding of the language, they're just going to show a person how much the person has researched the language. What exactly is "Post Query" anyway? I'm a JavaScript and PHP developer and I have no clue what this means. Does it refer to POST/GET (forms)? Or perhaps a framework? These questions are pretty vague as well. Asking a person what the "isNaN" function does is absolutely ridiculous; it's just a function and does not give an insight in to how a person would cope in a programming environment.
You want to see how people write and plain things out, not ask stupid questions. Every professional programmer has a portfolio, the portfolio is a sample of the creative process. For example the software development life cycle. Flow charts, coding structure. Skill and general knowledge of the programming language will grow and develop with time, but project management and team work flow skills are the most important.