Question

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?

Answer 1

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 for plain objects (keep reading for an alternative) are things that return arrays of property keys (which you can then get length from):

• Object.keys – Returns an array of the object’s own, enumerable, string-keyed properties.
• Object.getOwnPropertyNames – Like Object.keys, but includes non-enumerable properties as well.
• Object.getOwnPropertySymbols – Like Object.getOwnPropertyNames, but for Symbol-keyed properties instead of string-keyed properties.
• Reflect.ownKeys – Returns an array of an object’s own properties (whether or not they’re enumerable, and whether they’re keyed by strings or Symbols).

For instance, you could use Reflect.ownKeys like this:

var quesArr = new Array(); // Keep reading, don't do this
quesArr["q101"] = "Your name?";
quesArr["q102"] = "Your age?";
quesArr["q103"] = "Your school?";
console.log(Reflect.ownKeys(quesArr).length); // 4 -- includes the built-in
                                              // `length` property!

Notice that showed 4, not 3, because of the built-in length property of arrays. Since you don’t seem to be using the Array features of the object, don’t make it an array. You could make it a plain object:

const questions = {};
questions["q101"] = "Your name?";
questions["q102"] = "Your age?";
questions["q103"] = "Your school?";
// Or just:
// const questions = {
//    q101: "Your name?",
//    q102: "Your age?",
//    q103: "Your school?",
// };
console.log(Reflect.ownKeys(questions).length); // 3

But since you want to know how many things are in it, you might consider using a Map, because unlike objects, Map instances do have a property telling you how many entries they have in them: size.

const questions = new Map();
questions.set("q101", "Your name?");
questions.set("q102", "Your age?");
questions.set("q103", "Your school?");
// Or you can pre-fill the `Map` by passing an array of `[name, value]` arrays:
// const questions = new Map([
//     ["q101", "Your name?"],
//     ["q102", "Your age?"],
//     ["q103", "Your school?"],
// ]);
console.log(questions.size); // 3