What is the first class function in JavaScript ?

First-Class Function

A programming language is said to have First-class functions if functions in that language are treated like other variables. So the functions can be assigned to any other variable or passed as an argument or can be returned by another function. JavaScript treats function as a first-class citizen. This means that functions are simply a value and are just another type of object.

Usage of First-Class Function

• It can be stored as a value in a variable.
• It can be returned by another function.
• It can be passed into another function as a parameter.
• It can also stored in an array, queue, or stack.
• Also, It can have its own methods and property.

Example 1: Let us take an example to understand more about the first-class function.

Javascript

const Arithmetics = {
    add: (a, b) => {
        return `${a} + ${b} = ${a + b}`;
    },
    subtract: (a, b) => {
        return `${a} - ${b} = ${a - b}`
    },
    multiply: (a, b) => {
        return `${a} * ${b} = ${a * b}`
    },
    division: (a, b) => {
        if (b != 0) return `${a} / ${b} = ${a / b}`;
        return `Cannot Divide by Zero!!!`;
    }

}

console.log(Arithmetics.add(100, 100));
console.log(Arithmetics.subtract(100, 7))
console.log(Arithmetics.multiply(5, 5))
console.log(Arithmetics.division(100, 5));

Output

100 + 100 = 200
100 - 7 = 93
5 * 5 = 25
100 / 5 = 20

Note: In the above example, functions are stored as a variable in an object.

Example 2: This example shows more about the first-class function.

Javascript

const Geek = (a, b) => {
    return (a + " " + b);
}

console.log(Geek("Akshit", "Saxena"));

Output

Akshit Saxena