JavaScript Interview Questions

Give a high level overview of how JavaScript interacts with the DOM.

What are some different ways that JavaScript code can be embedded into or linked into an XHTML page?

Are objects passed by value or by reference? Does the type of object matter?

Is JavaScript an object-oriented language? Why or why not?

What is your favorite way to debug JavaScript?

What is JSON? What are some common uses of JSON?

What is the difference between undefined and null?

What does the isNaN() function do?

What will the following code do?

function printMe() { var b = 5; alert (a+b); }
var a = 3; var b = 2;
printMe();
alert(a+b);

What is a for…in loop?

What is the difference between window.onload and onDocumentReady? Which are you (typically) more likely to use?

What are a few different ways to attach handlers (e.g. click, blur, etc.) to a DOM element? Are any better than the others?

What's unique about functions in JavaScript? (The answer you're looking for here is that they're first class objects; e.g. you can pass a function as an argument to another function, just like you could pass an object. Explore this concept with the interviewee to see how much they know.)

What's an anonymous function?

What is JavaScript namespacing? Why would you want to use it?

Basic: what is jQuery?

How do you select a DOM element (or elements) in jQuery?

What does it mean to chain functions in jQuery?