Functions : first class objects

Interview Questions

Functions are first-class objects in JS. They possess all the capabilities of objects and are thus treated like any other object in the language. So, we can say that functions are first-class objects.

They can be:

  • Created via literals 
    1
2
3

    function ninjaFunction() {
  // something happens here
}
  • Assigns a new function to a variable 
    1
2
3

    var ninjaFunction = function() {
  // something happens here
};
  • Adds a new function to an array 
    1
2
3

    ninjaArray.push(function(){
  // something happens here
});
  • Assigns a new function as a property of another object 
    1
2
3

    ninja.data = function(){
  // something happens here
};
  • Passed as arguments to other functions 
    1
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3
4

    function call(ninjaFunction){ 
  ninjaFunction();
} 
call(function(){});
  • Returned as values from functions 
    1
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3

    function returnNewNinjaFunction() { 
  return function(){}; 
}
  • They can possess properties that can be dynamically created and assigned: 
    1
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3
4

    var ninjaFunction = function(){
  // something happens here
}; 
ninjaFunction.name = "Hanzo";

Whatever we can do with objects, we can do with functions as well. Functions are objects, just with an additional, special capability of being invokable:

Functions can be called or invoked in order to perform an action.

Interview questions

Q1. What do you mean by first class objects in JavaScript?