javascript - What is meant by 'first class object'?

Question

In a recent question, I received suggestions to talk on, amongst other things, the aspect of JavaScript where functions are 'first class' objects. What does the 'first class' mean in this context, as opposed to other objects?

EDIT (J?rg W Mittag): Exact Duplicate: "What is a first class programming construct?"

Answer 1

To quote Wikipedia:

In computer science, a programming language is said to support first-class functions (or function literal) if it treats functions as first-class objects. Specifically, this means that the language supports constructing new functions during the execution of a program, storing them in data structures, passing them as arguments to other functions, and returning them as the values of other functions.

This page also illustrates it beautifully:

Really, just like any other variable

• A function is an instance of the Object type
• A function can have properties and has a link back to its constructor method
• You can store the function in a variable
• You can pass the function as a parameter to another function
• You can return the function from a function

also read TrayMan's comment, interesting...