Traditional Functions or Arrow Functions in Javascript?

#discuss #beginners #javascript #webdev

Recently, I started my Web Dev journey, and these days I have been reading about functions in Javascript. I've noticed that there are many ways to declare a function. Two of them caught my attention though, which are Traditional Functions and Arrow Functions.

I have read about them and in my understanding, I have to take into consideration the following:

Traditional Functions	Arrow Functions
No matter where you declare and call the function, Hoisting is the key.	The order matters. Declare it into a variable and then call it.
Once you declare it, you won't lose it.	The code seems cleaner than a traditional declaration.
	Once you override the variable where the function lives, it's over.

So, I would like to put on the table this topic in order to clarify my mind a little bit more about it, and comprehend the best use case for each of them.

Which one do you usually use when you code functions in Javascript?

Top comments (11)

Thomas Step • Oct 30 '19

The order matters. Declare it
into a variable and then call it.

I might be incorrectly interpreting what you're saying, but have you heard of IIFE? developer.mozilla.org/en-US/docs/G...
You can create a function and immediately call it while storing the result in a variable.

Jose Arteaga • Oct 30 '19

Exactly! It was more related to hoisting. I mean, there must be an error if I call the function expression before its declaration. Otherwise with traditional functions it won't happened.

By the way, thanks for the information about IIFE, I will read up on it.

Thomas Step • Oct 31 '19

I definitely misunderstood the first time through so I apologize for that.

Jose Arteaga • Oct 31 '19

There's no problem Thomas! Thank you for your response and help.

SavagePixie • Oct 30 '19

I think the author was referring to the fact that function expressions aren't hoistered.

Ed Reeseg • Oct 30 '19

I use them pretty interchangeably these days - I like the traditional syntax for how self-explanatory it is (though, these days, I think most people are just as familiar with ES6 arrow syntax).

As Ben mentioned previously, one of the main draws of arrow syntax has to do with how it interacts with the this keyword. It does not generate its own context for this, but rather inherits the context of the environment in which it was created.

For things like React class components, this can be a godsend.

class Test extends React.Component {
  constructor(props){
    this.log = this.log.bind(this);
  }
  log(){
    console.log(this);
  }
  render(){
    return // Whatever
  }
}

vs.

class Test extends React.Component {
  log = () => console.log(this);
  render(){
    return // Whatever
  }
}

Of course, with more people being familiar with the convenience of Hooks, this is a bit less relevant. Still good to note.

Jose Arteaga • Oct 30 '19

Right! I was reading more about it and I found what you mentioned about the this keyword. I'm not familiar yet with this concept, but I will read up on it. For sure there should be an advantage using the arrow syntax. Thanks Ed!

SavagePixie • Oct 30 '19 • Edited

Once you override the variable
where the function lives, it's over.

If you assign them to a constant, you don't run the risk of overriding them. In general, it's a good idea to always use the keyword const if you want to store your function expressions.

Generally I favour expressions over declarations because they are shorter to type. When written as callbacks, they also seen clearer to me.