What is first class, higher order, and callbacks in javascript?

In this question we will briefly understand what is first order, higher order, and callback functions.

Let’s consider below code.

function Message(msg){
    console.log('Message is:'+msg);
}
function Print(message){
    message("testing message");
}
Print(Message);

Note here that function Print is taking the function Message as a input function having expectation that internally Print function will call the Message function. in javascript such functions are commonly called as callback functions.

Here, Print function is taking another function as it’s argument hence Print function is called higher order function.

Callback function has extensive usage in javascript. It permits the caller function to invoke the callback function whenever it is needed.

- First class/ Order / Anonymous function :

var a = function () {
    console.log("First order or Anonymous function")
}
a()

a is variable here and it holds a function. Here, a is called as first order/class functions.

1 Answer

First Class: The JavaScript First-Class functions are the functions which you can apply as a value to another variable or functions directly. The First-Class functions is simply acts as a value. Following is an Example. Const Calculation = { addition:(first, second) => { return `${first} ${second} = ${first second}`; }, subtraction:(first, second) => { return `${first} - ${second} = ${first-second}` }, } const addresult=Calculation.addition(100, 20) const subresult=Calculation.subtraction(100, 15) console.log(Calculation.addition(100, 100)); console.log(Calculation.subtraction(100, 7)); Higher-Order: The higher order functions are the functions which receives another functions as argument or return new function in result . This both condition calls as a higher order functions and this condition is dependent on the First-Class function. Following is an example ..... Const message = function(name){ return function(msg){ console.log(`Hi!! ${name}, ${msg}`); } } const welcome_message = message('Manish'); welcome_message("Welcome To C-Sharp Corner") Call backs : The function call back takes another function as an argument and call it once the execution of the current function is over. Following is an example. function alertSum(result) { alert(result); } function Calculate(first, second, callBackArgument) { let sum = first second; callBackArgument(sum); } Calculate(5, 5, alertSum);

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