Node JS Tutorial - Function Expressions

In this tutorial, we will learn about function expressions in JavaScript. A JavaScript function can be defined using an expression, which can be stored in a variable. After a function expression has been stored in a variable, the variable can be used as a function.

Creating a Function Expression

Let's create a function expression. Go to your project and inside the index.js file, remove all the existing lines and create a variable. Let's say the variable name is `message`. Inside this message variable, assign a function by typing:

var message = function(){ 
    return `Hello World!`; 
}

This is a function expression, where the function name is omitted. Now, let's call this message variable like a function:

console.log(message()); 

Let's run this code. Go to the command prompt and type:

node index.js

You can see the output `Hello World`.

Using Function Expressions as Arguments

We can also use function expressions as arguments. Let's see an example. Create another expression function:

var sum= function(a,b) 
{ 
    return a+b; 
}

This is a sum expression function that returns the sum of two numbers.

Now, create another function that uses a function as a parameter:

var calculateSum = function(fun) 
{ 
    return fun(); 
}

Call this calculate sum function and pass the sum function as an argument:

calculateSum(sum(5,6)); 

Let's check the result, and you can see the output 11.

In this way, you can create and use function expressions in Node.js.