Arrow functions in Javascript

Javascript Front End Technology Object Oriented Programming

According to MDN, An arrow function expression is a syntactically compact alternative to a regular function expression, although without its own bindings to the this, arguments, super, or new.target keywords. Arrow function expressions are ill-suited as methods, and they cannot be used as constructors.

There are 3 subtle differences in regular functions and arrow functions in JavaScript.

No own this binding
Arrow functions do not have their own value. The value of this inside an arrow function is always inherited from the enclosing scope.

Example

this.a = 100;
let arrowFunc = () => {this.a = 150};
function regFunc() {
   this.a = 200;
}
console.log(this.a)
arrowFunc()
console.log(this.a)
regFunc()
console.log(this.a)

Output

This will give the output −

100
150
150

See that the arrow function changed this object outside its scope. The regular function just made the changes within its own.

Arrow functions do not have a arguments array In JS arguments array in functions is a special object that can be used to get all the arguments passed to the function. Similar to this, arrow functions do not have their own binding to a arguments object, they are bound to arguments of enclosing scope.
Arrow functions are callable but not constructible If a function is constructible, it can be called with new, i.e. new User(). If a function is callable, it can be called without new (i.e. normal function call).

Functions created through function declarations / expressions are both constructible and callable.

Arrow functions (and methods) are only callable. class constructors are only constructible.

If you are trying to call a non-callable function or to construct a nonconstructive function, you will get a runtime error.

Example

let arrowFunc = () => {}
new arrowFunc()

Output

This code gives the error −

arrowFunc is not a constructor

Ayush Gupta

Updated on 27-Nov-2019 09:57:51

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