Tag Archives: Object

Object Reflection In JavaScript

Reflection is a powerful technique that I’ve used a lot in C#. On several occasions I’ve found some uses for this technique in JavaScript too. Most recently, I was writing a test harness for a RESTFul web service to allow our QA folks a easy way to test it. Typically, when I’m writing these kinds of things I have a couple objectives in mind.

First, I don’t want to turn the testing tool into a maintenance item. That is, if there are updates to the software being tested (a web service in this case) I don’t want to have to update the tool.

Second, I don’t want to add another uncontrolled variable to the testing.   Meaning, I don’t want the testing tool to require extensive QA or to create a layer of possible bugs to be validated anytime QA finds an issue with the software being tested.

Finally, I don’t want to spend a lot of time on it and I’d like to reuse it. It’s an internal tool that is usually being used by a semi-technical person and has a very specific purpose, being pretty isn’t one of them. And, if I can use it again, for another web service in this case, double bonus!

In the case of the RESTFul Web Service testing tool I accomplished this in two ways.

First, I build the inputs for the service by parsing the web service schema (.xsd) dynamical. This way, if new inputs are added I don’t have to update the testing tool. I probably write a post on that part another day.

Second, I output the results (which are returned in JSON) to a web page using reflection after the JSON object is parsed to a JavaScript object.

Here is an example of how I do it:

Consider the following object. It has a set of properties, a nested object, and a function.

var obj = new Object;
obj.FirstName = “John”;
obj.LastName = “Smith”;
obj.FullName = “John Smith”;
obj.Address = “Main Street”;
obj.Phone = “999-999-9999”
obj.GetName = (function () {});
obj.History = new Object();
obj.History.PreviousAddress = “South Street”;
obj.History.PreviousPhone = “888-888-8888”;

All I want to do is print each property and it’s value to the screen. And, if there is a nested object I want to print it’s properties too. This will allow the return results to be validated.

To do this I use a script like this:

function DisplayObjectProperties(obj) {
for (prop in obj) {
var text = “”
if(typeof obj[prop] != “function” && typeof obj[prop] != “object”){
text = prop + “: ” + obj[prop];
else if (typeof obj[prop] === “object”) {
$(“body”).append(“<div>”+ text + “</div>”);

Nothing too much going on here, just a loop through the object and appending each property name and it’s value to an html element.  The important thing is to test the type, so you can handle nested objects, arrays, functions, etc however you might want to.  In my case, if there is a nested object I want to display it’s properties too.  I do that with a recursive call to the function passing the nested object.

Call it:  Just pass the object to the function it will do the rest.



FirstName: John
LastName: Smith
FullName: John Smith
Address: Main Street
Phone: 999-999-9999
PreviousAddress: South Street
PreviousPhone: 888-888-8888

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