Question

What are expando objects in javascripts?

For what purpose we need this ? Any complete example will be appreciated

I found 1 article here Javascript: The red-headed stepchild of web development

Answer 1

Well, in javascript, any object is an expando object. What it means is, as the article covers, that whenever you try to access a property¹ it will automatically be created.

var myObj = {}; // completely empty object
myObj.myProp = 'value';

The moment you assign myProp a value, the property myProp is dynamically created, eventhough it didn’t exist before. In a lot of other languages, such as C#, this is not normally possible (actually C# has just enabled expando object support as well, but that’s besides the point). To access a property in a normal class in C#, you need to specify in the class that it does indeed have this property.

¹ Not quite correct. See npup’s comment below for clarification.