The JavaScript Arrow function lacks its own "this" context and does not possess any arguments. Therefore, utilizing it as an event handler, a method in an object literal, or a prototype method is generally discouraged. When a function requires the use of the arguments object, arrow functions do not operate as intended. There is no need to utilize the function keyword to define an arrow function, as it does not yield any return value. Additionally, arrow functions cannot be employed as constructors.
Reasons not to Use the Arrow Function
There are three reasons not to Use Arrow Functions in JavaScript.
- Event handlers
- Object methods
- Prototype methods
- Functions use the arguments object
Event Handlers
The event handler does not yield any input value and operates using the data from the object. In instances where the arrow function fails to return a value, it results in an undefined output.
Why do event handlers not use an arrow function?
- The "this.value" function in the event handler always returns undefined as an output.
- Global object in a web browser is used window. The value is a property which is missing from the window object. As a result, the window object has the value property added to the function. These values are set to "undefined" by the JavaScript engine.
- There is no "this" value specific to the arrow function. The surrounding global scopes are used for the "this" keyword value. The global object is referred to by the "this" value in the arrow function in the example below.
- You can use a standard function in the place to resolve the problem. The element acts as the event's trigger when the "this" value is tied to it.
Example:
The subsequent example illustrates the concept of an undefined value through the use of the arrow function method. However, this approach is ineffective when applied to the event handler method within the arrow function context.
<!DOCTYPE html>
<html>
<head>
<title>
When You Should Not Use Arrow Functions in JavaScript
</title>
<style>
#demo1 {
background-colour: orange;
border: 1px solid black;
width: 370px;
}
</style>
</head>
<body>
<div id = "demo1">
<h3>
When You Should Not Use Arrow Functions in JavaScript
</h3>
<p>
Event handlers do not work for the arrow function
</p>
<input type = "text" name = "usernames" id = "usernames" placeholder = "Enter a usernames">
<p id = "greetings"></p>
</div>
<script>
const greeting = document.querySelector('#greetings');
const username = document.querySelector('#usernames');
username.addEventListener('keydown', () => {
greeting.textContent = 'javascript tutorial: Hello ' + this.value;
});
</script>
</body>
</html>
Output
The result illustrates the undefined value in JavaScript.
Object Methods
The Prototype method utilizes the function to access the data of its own value. It is important to note that this keyword is not applicable when dealing with arrow functions.
Example:
The subsequent illustration demonstrates the NaN value utilizing the arrow function approach. However, this method is ineffective when applied to the event handler technique within the arrow function.
<!DOCTYPE html>
<html>
<head>
<title>
When You Should Not Use Arrow Functions in JavaScript
</title>
<style>
#demo1 {
background-colour: orange;
border: 1px solid black;
width: 370px;
}
</style>
</head>
<body>
<div id = "demo1">
<h3>
When You Should Not Use Arrow Functions in JavaScript
</h3>
<p>
Object methods do not work for the arrow function
</p>
<input type = "text" name = "usernames" id = "usernames" placeholder = "Enter a usernames">
<p id = "greetings"></p>
</div>
<script>
const greeting = document.querySelector('#greetings');
const username = document.querySelector('#usernames');
username.addEventListener('keydown', () => {
const counter = {
count: 0,
next: () => ++this.count,
current: () => this.count
};
greeting.textContent = 'javascript tutorial: Hello ' + counter.next();
console.log(counter.next());
});
</script>
</body>
</html>
Output
The output shows the NaN value in JavaScript.
Solution of the object methods problem:
We can utilize straightforward functions to implement the object functions technique.
Example:
The subsequent example operates correctly without encountering any errors.
<!DOCTYPE html>
<html>
<head>
<title>
When You Should Not Use Arrow Functions in JavaScript
</title>
<style>
#demo1 {
background-colour: orange;
border: 1px solid black;
width: 370px;
}
</style>
</head>
<body>
<div id = "demo1">
<h3>
When You Should Not Use Arrow Functions in JavaScript
</h3>
<p>
Object methods work for the arrow function
</p>
<input type = "text" name = "usernames" id = "usernames" placeholder = "Enter a usernames">
<p id = "greetings"></p>
</div>
<script>
const greeting = document.querySelector('#greetings');
const username = document.querySelector('#usernames');
username.addEventListener('keydown', () => {
const counter = {
count: 0,
next() {
return ++this.count;
},
current() {
return this.count;
}
};
greeting.textContent = 'javascript tutorial: Hello ' + counter.next();
console.log(counter.next());
});
</script>
</body>
</html>
Output
The output shows the data of the function.
Prototype Methods
The prototype method employs the function to utilize its own value data. However, the multiple function is incompatible with the arrow function.
Example:
The subsequent example illustrates the concept of undefined values when utilizing the arrow function syntax. It is important to note that this approach is ineffective with the prototype method within arrow functions.
<!DOCTYPE html>
<html>
<head>
<title>
When You Should Not Use Arrow Functions in JavaScript
</title>
<style>
#demo1 {
background-colour: orange;
border: 1px solid black;
width: 370px;
}
</style>
</head>
<body>
<div id = "demo1">
<h3>
When You Should Not Use Arrow Functions in JavaScript
</h3>
<p>
The prototype method does not work for the arrow function
</p>
<input type = "button" name = "usernames" id = "usernames" value = "Click the button">
<p id = "greetings"></p>
</div>
<script>
const greeting = document.querySelector('#greetings');
const username = document.querySelector('#usernames');
username.addEventListener('click', () => {
function MyName(name) {
this.personName = name;
}
MyName.prototype.sayPersonName = () => {
console.log(this === window); // => true
return this.catName;
};
const person = new MyName('Mew');
person.sayPersonName();
greeting.textContent = 'javascript tutorial: Hello ' +person.sayPersonName();
});
</script>
</body>
</html>
Output
The output displays the notion of an undefined value in JavaScript.
Solution of the Prototype methods problem
We can employ straightforward functions to utilize the prototype functions method effectively.
Example:
The subsequent example operates correctly without encountering any errors.
<!DOCTYPE html>
<html>
<head>
<title>
When You Should Not Use Arrow Functions in JavaScript
</title>
<style>
#demo1 {
background-colour: orange;
border: 1px solid black;
width: 370px;
}
</style>
</head>
<body>
<div id = "demo1">
<h3>
When You Should Not Use Arrow Functions in JavaScript
</h3>
<p>
The prototype method does not work for the arrow function
</p>
<input type = "button" name = "usernames" id = "usernames" value = "Click the button">
<p id = "greetings"></p>
</div>
<script>
const greeting = document.querySelector('#greetings');
const username = document.querySelector('#usernames');
username.addEventListener('click', () => {
function MyPerson(name) {
this.catName = name;
}
MyPerson.prototype.sayPersonName = function() {
console.log(this === person); // => true
return this.catName;
};
const person = new MyPerson('Student');
person.sayPersonName(); // => 'Student'
greeting.textContent = 'javascript tutorial: Hello ' +person.sayPersonName();
});
</script>
</body>
</html>
Output
The output shows the data of the function.
Functions Use the Arguments Object
The arguments object is not available in arrow functions. Consequently, if your function relies on parameter objects, you are unable to use an arrow function.
Example:
The subsequent illustration demonstrates the error value when employing the arrow method. This approach is ineffective for the prototype method within the arrow function. The failure of the function is attributed to the argument object.
<!DOCTYPE html>
<html>
<head>
<title>
When You Should Not Use Arrow Functions in JavaScript
</title>
<style>
#demo1 {
background-colour: orange;
border: 1px solid black;
width: 370px;
}
</style>
</head>
<body>
<div id = "demo1">
<h3>
When You Should Not Use Arrow Functions in JavaScript
</h3>
<p>
Functions use the arguments object does not work for arrow function
<br>
console.log tab shows the error of the concat() function
</p>
<input type = "button" name = "usernames" id = "usernames" value = "Click the button">
<p id = "greetings"></p>
</div>
<script>
const greeting = document.querySelector('#greetings');
const username = document.querySelector('#usernames');
username.addEventListener('click', () => {
const concat = (separator) => {
let args = Array.prototype.slice.call(arguments, 1);
return args.join(separator);
console.log(concat());
}
greeting.textContent = 'Uncaught ReferenceError: arguments is not defined';
console.log(concat());
});
</script>
</body>
</html>
Output
The output shows the error value in javascript.
Solution of the argument objects problem:
A straightforward function can be utilized to manipulate the arguments object.
Example:
The example provided operates correctly without encountering any errors.
<!DOCTYPE html>
<html>
<head>
<title>
When You Should Not Use Arrow Functions in JavaScript
</title>
<style>
#demo1 {
background-colour: orange;
border: 1px solid black;
width: 370px;
}
</style>
</head>
<body>
<div id = "demo1">
<h3>
When You Should Not Use Arrow Functions in JavaScript
</h3>
<p>
Functions use the arguments object works for arrow function
<br>
Remove the error of the argument object
</p>
<input type = "button" name = "usernames" id = "usernames" value = "Click the button">
<p id = "greetings"></p>
</div>
<script>
const great_data = document.querySelector('#greetings');
const username = document.querySelector('#usernames');
username.addEventListener('click', () => {
function concat(separator) {
let args = Array.prototype.slice.call(arguments, 1);
return args.join(separator);
}
great_data.textContent = 'Hello student' +concat();
console.log(concat());
});
</script>
</body>
</html>
Output
The output shows the data of the function.
Conclusion
JavaScript does not directly utilize the arrow function for managing user validation and operations.