Arrow Functions in JavaScript

Arrow Functions in JavaScript

Arrow functions in JavaScript are a concise alternative way to write regular functions in JavaScript. They are also called "fat arrow functions" as they use a fat arrow (=>). It got its name arrow functions due to using a fat arrow.

In arrow functions, instead of the function keyword, a fat arrow is used. Let's see how the above regular function can be written using the fat arrow function.

// Declaring and calling an arrow function

const hello = () => {
    console.log("Hey Ninjas!");
}

hello();

Output:

JavaScript does not allow a line break between the parameter definition and the fat arrow in an arrow function. 

For example,

const hello = () 
=> {
    console.log("Hey Ninjas!");
}

hello();

Output:

However, the following code works perfectly fine:

const hello = () => {
    console.log("Hey Ninjas!");
}

hello();

Output:

No Arguments

If an arrow function doesn't take any argument, then use empty parentheses. For example,

// Arrow functions with no arguments

const result = () => 20; 
console.log(result());

Output:

Note: The above code is the same as,

// Arrow functions with no arguments

const result = () => {
   return 20;
}
console.log(result());

Output:

Passing One Argument

We can omit the parentheses if an arrow function has only one argument. For example,

// Arrow function with one argument

const result = num => num + 5;
console.log(result(10));

Output:

Passing Multiple Arguments

We cannot omit the parentheses if an arrow function has more than one argument. For example,

// Arrow function with multiple arguments

const result = (num1, num2) => num1 + num2;
console.log(result(10, 5));

Output:

Multiline Arrow Function

If an arrow function has multiple statements in the code block, we cannot omit the curly braces and return the keyword. For example,

// Multiline arrow function

const result = (num1,num2) => {
   let total = num1 + num2;
   return total;
}

console.log(result(10, 5));

Output:

Using this keyword

Inside a regular function, the ‘this’ keyword refers to the function where it is called. However, when this keyword is used with the arrow function, it refers to its parent scope. This happens because the arrow function doesn't define its own execution context and does not have its own "this".

Let's look at an example for a better understanding.

// Regular function

function Student() {
   this.name = 'Sapna',
   this.introduce = function () {
   
       // Here this is accessible
       console.log(this.name);
       function innerIntroduceFunc() {
       
           // Here this refers to the global object
           console.log(this.name);
       }
       innerIntroduceFunc();
   }
}

let s = new Student();
s.introduce();

Output:

Here, this.name inside this.introduce() is accessible because this.introduce() is the method of an object.

However, innerIntroduceFunc() is a normal function, and this.name is not accessible because this refers to the global object. Hence, this.name inside the innerFunc() function gives undefined.

// Arrow function

function Student() {
   this.name = 'Sapna',
   this.introduce= function () {
       console.log(this.name);
       
       // Keyword ‘this’ refers to parent scope
       let innerIntroduceFunc = () => {
           console.log(this.name);
       }
       innerIntroduceFunc();
   }
}

const s = new Student();
s.introduce();

Output:

Here, the innerIntroduceFunc() is defined using the arrow function. So, this refers to the parent's scope. 

Argument Binding

Regular functions in JavaScript have arguments binding. Due to this, we can access the arguments passed using the arguments keyword. 

However, arrow functions in JavaScript do not have arguments binding. So, when we try to access an argument using the arrow function in JavaScript, it gives us an error. For example,

let func = () => {
   console.log(arguments);
}
func(1,2,3);

Output:

To solve this issue, we can make use of the spread operator.

let func = (...arguments) => {
   console.log(arguments);
}
func(1,2,3);

Output:

Promises and Callbacks

While writing promises and callbacks, arrow functions provide a better syntax. For example, 

const ninjaTest = async () => {
  return "Hello";
}

ninjaTest().then(
  function (value) {
    console.log("Success!");
  },
  function (error) {
    console.log("Error!");
  }
);

Output:

Object Literals

We can use the arrow functions to declare setter functions and set the value of object literals effortlessly. Let's look at an example.

// Object literal setter using regular functions

const setStudentDetail = function (rollNo, name) {
  return {
    rollNo: rollNo,
    name: name,
  };
};

console.log(setStudentDetail(1, "Sapna"));

Output:

// Object literal setter using arrow functions

const setStudentDetail = (rollNo, name) => ({ rollNo: rollNo, name: name });
console.log(setStudentDetail(1, "Sapna"));

Output:

Advantages

Some of the benefits of using arrow functions in JavaScript are as follows:

• Arrow functions have shorter syntax than regular function expressions.
   
• Arrow functions have implicit return statements.
   
• Arrow functions increase readability.

Limitations

Some of the limitations of arrow functions are as follows:

• Arrow functions are anonymous and can be harder to debug. However, we can assign them to a variable for more clarity.
   
• Arrow functions cannot be used as constructors.
   
• Arrow functions do not have new.target keyword.
   
• Arrow functions don't have their own bindings to this or super. Also, they should not be used as methods.
   
• We usually cannot use an arrow function as a method.
   
• Arrow functions cannot be used as a generator function.
   
• The call, apply and bind methods cannot be used with arrow functions.
   

Check out this article - Balanced Parentheses and Fibonacci Series in JavaScript

Frequently Asked Questions

When can we omit return in arrow functions?

Return can be omitted when there are no curly brackets. This is because arrow functions use implicit returns when written without curly brackets. In contrast, we have to use return explicitly when there are curly brackets.

Does an arrow function have a prototype property? 

The function has the prototype property when a function is defined by the regular method using a function keyword. However, arrow functions in JavaScript don't have the prototype property.

Where are arrow functions often used?

Arrow functions are frequently used in promise chaining, callback chaining, array methods, and situations where anonymous functions would be useful.

How to make arrow functions in JavaScript asynchronous?

We can make an arrow function asynchronous by using async/await.

Why can arrow functions not be used as generators?

We cannot use the yield keyword within an arrow function's body. Hence, arrow functions cannot be used as generators.

Conclusion

This article discusses the topic of Arrow functions in JavaScript. In detail, we have seen the definition of arrow functions, this keyword, argument binding, promises and callbacks, Object literals, advantages and limitations.

We hope this blog has helped you enhance your knowledge of Arrow functions in JavaScript. If you want to learn more, then check out our articles.

• Basics of JavaScript
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• Array Methods in JavaScript
• JavaScript Numbers
• Fibonacci Series in Java
• Introduction to PHP
• Introduction to Javascript

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