Length of a JavaScript associative array

I have a JavaScript associative array (or some may prefer to call it an object) like, say

var quesArr = new Array();
quesArr["q101"] = "Your name?";
quesArr["q102"] = "Your age?";
quesArr["q103"] = "Your school?";

Is there a built-in function that could get the length of this array, or a solution in jQuery or another library? Currently quesArr.length would give 0, as most of you must be knowing.

Please don’t suggest iterating over the entire array/object as mentioned in this question, because the array/object which I have is very large.

Is there a way I could proceed with this?

No, there is no built-in property that tells you how many properties the object has (which is what you're looking for).

The closest I can think of are two ES5 and higher features, Object.keys (spec | MDN) and Object.getOwnPropertyNames (spec | MDN). For instance, you could use Object.keys like this:

console.log(Object.keys(quesArr).length); // "3"

Object.keys returns an array of the names of an object's own enumerable string-named properties. But internally (in theory) it's that loop you didn't want to use (and the polyfill for it for pre-ES5 environments uses a loop, of course). If you also want non-enumerable string-named properties, you'd use Object.getOwnPropertyNames instead.

In ES2015+, an object can have properties whose keys are Symbols rather than strings. Object.getOwnPropertySymbols (spec | MDN) lets you get them.

FWIW, unless you're going to use the Array features of the object, don't make it an array. Instead:

var quesArr = {};
quesArr["q101"] = "Your name?";
quesArr["q102"] = "Your age?";
quesArr["q103"] = "Your school?";

Those keys don't have to be given as string literals in square brackets, either, if you don't want them to be (whether you use an array or a plain object):

var quesArr = {};
quesArr.q101 = "Your name?";
quesArr.q102 = "Your age?";
quesArr.q103 = "Your school?";

But you can use the other notation if you prefer; they're exactly equivalent except that with dotted notation the keys must be valid identifier names (in bracketed notation they can be anything).

You can even do this:

var quesArr = {
    q101: "Your name?",
    q102: "Your age?",
    q103: "Your school?"
};

or (if the keys won't be valid identifiers):

var quesArr = {
    "q101": "Your name?",
    "q102": "Your age?",
    "q103": "Your school?"
};

Those can be single or double quotes.

Suppose you have the following,

var myObject = {};  // Denotes an Object is being created
myObject.city = "Chennai";
myObject.state = "Tamilnadu";
myObject.country = "Indian Peninsula";
console.log(myObject.length);  // Results in undefined

But, there is a way to calculate the length in modern browsers (Chrome, Firefox 4+, and Internet Explorer 9):

Object.keys(myObject);
// --> ["city", "state", "country"]
Object.keys(myObject).length
// --> 3