Functions in a React Native Component (function vs const function)

user_5138815 0
Viewed 873

This is probably super simple but I can't quite word how to search for an answer.

I've just noticed I have functions in my react native components that sometimes I declare with const while others I don't and there seems to be no difference.

Like so

const MyComponent = (props) => {
 
     const myFunction = () => {
        console.log("Hello world");
     }
     return(
         <TouchableOpacity onPress={myFunction}>
            ...somestuff
         </TouchableOpacity>
     )
}

or

const MyComponent = (props) => {
 
     myFunction = () => {
        console.log("Hello world");
     }
     return(
         <TouchableOpacity onPress={myFunction}>
            ...somestuff
         </TouchableOpacity>
     )
}

I can't find anything different between them in terms of output. Is this just the compiler saving my a*s or is there actually a difference between them?

react-native reactjs function-declaration function
2 Answers

I don't think in react native it matters because of it's lifecycles. But in normal javascript it has a difference in hoisting. Without const you can call a function that hasn't been declared:

doTheThing();


function doTheThing() {
   console.log(`This is awesome number ${getAwesome()}`)
}

function getAwesome() {
  return (+((Math.random() * 10000).toString().split('.')[0]))
}

With Const/let it doens't let you do that:

 const tryDoTheThing = () => {
    console.log(`This is me trying to be awesome ${getAwesome()}`)
 }


 // "getAwesome is not defined", because it is referenced too early
 tryDoTheThing() // comment to see the rest work


 const getAwesome = () => (+((Math.random() * 10000).toString().split('.')[0]))


 const doTheThing = () => {
   console.log(`This is awesome! ${getAwesome()}`)
 }

 doTheThing() // prints

using function will put it's declaration on top of the current scope (to the top of the current script or the current function).

user_103108080

Javascript won't stop you from using undeclared variables.

x = 10; // This is completely fine, as it'll be added in global scope

To avoid doing this, generally use strict is used.

"use strict";
x = 10;       // This will cause an error because x is not declared
user_98058100
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