Difference between arrow and normal functions in JavaScript

In this tutorial we are going to see how arrow functions differ from normal JavaScript functions. We will also see when you should use one and when you should use the other.

Normal functions

JavaScript's standard functions, those we call normal or standard functions, have been included in JavaScript since its inception. They are created by means of the declaration function, then indicating the name of the function and an opening and closing parenthesis, between which we can define the possible parameters that the function receives. Here is an example:

function myfunction() {    
      // code  
}

If you wanted to invoke one of these functions, like the one in our example, you would have to call it this way:

myfunction();

Además también es posible asignar cualquier función a una variable, tal y como hacemos en este ejemplo:

const  myfunction() = function myfunction() {    

// Code   

}    

 myfunction()();

If you prefer, you can also declare these functions as anonymous, so that they are unnamed. The only difference between an anonymous function and a named function is that in case an error occurs, you will not see the name of the function in the trace that is displayed. Here is an example of an anonymous function:

const myfunction() = function () {    
// Code  }    
myfunction();

We can also pass parameters to the function regardless of how we declare it:

function myfunction(param1, param2) {    
// Code 
}    
myfunction('Hi Joe', 'Black');

Arrow functions

JavaScript arrow functions were introduced in the ES6 version of JavaScript, which appeared in 2015. They are something of an additional version with respect to normal functions. Like anonymous functions, they are nameless. You may assign them to a variable, but the name of the variable will be just that, the name of the variable, not the name of the function.

To declare these functions, you first declare a variable and then, after the possible parameters, you write the set of symbols =>, which are the representation of an arrow. The name of the arrow functions comes precisely from this symbol. After the arrow, the body of the function is placed between braces. Here is an example:

const myfunction = () => {    
// Code 
 }  
  
myfunction();

In case we have only one parameter, we can omit the parentheses:

const myfunction = param => {    
// Code  
}    
myfunction();

Otherwise, as when we have two or more parameters or when we have none, the parentheses are mandatory.

On the other hand, in case the function only includes one statement, it is possible to omit the braces of the function. In this case, it is understood that there is a return statement, so the result of the statement is returned by the function:

const myfunction = param => 'Hi Joe ' + param;  
myfunction('Black');

For more information, you can see in more detail how to use the arrow functions.

The differences

As we have seen, the differences in terms of syntax are quite large. However, for now they are not very different in terms of functionality. Moreover, both normal functions and arrow functions can be used as methods of any class using the same syntax.

However there is a rather big difference between the two types of function. We are talking about the treatment that each type of function makes of the this element in the body of the function. Let's propose the following example:

const shoes = {    
     brand: 'Camper',    
     model: 'boots',    
     buy: function() {      
        console.log(`Buy the ${this.brand} ${this.model}`);    
     },    
     stop: () => {      
       console.log(`Stop buying ${this.brand} ${this.model}`);    
     }  
}

The buy() function is a normal or standard function, while the stop() function is an arrow function. Let's see how this is treated in each case:

In the start() function, the reserved word this refers to the object, since this refers to the very scope in which the function is defined.

However, in the function stop(), the word this does not refer to the object, but refers to the scope in which the constant shoes is defined. That is, the parent context above the object.

In arrow functions, "this" does not refer to the instance of the object in which it is defined, but refers to the scope that this refers to externally. This means that arrow functions are not the best choice when defining a method on an object, since you will usually always want to have access to the object inside the function. In any other case, the use of arrow functions is recommended.

Janeth Kent

Licenciada en Bellas Artes y programadora por pasión. Cuando tengo un rato retoco fotos, edito vídeos y diseño cosas. El resto del tiempo escribo en MA-NO WEB DESIGN AND DEVELOPMENT.