Arrow function in javascript's replace function

Question

I have a very simple code that converts every letter to lower case and later sets upper case for every first letter using RegExp:

let quote = 'I dO nOT lIke gREen eGgS anD HAM';
let fixQuote = quote.toLocaleLowerCase('en-US');

let regex = /(^\w|\s\w)/g;

let fixedQuote = fixQuote.replace(regex, m => m.toUpperCase());

Can someone explain what does the arrow function m => m. does in this part? I don't understand what m stands for here.

Thanks!

It is explained in the [String#replace()](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/replace) docs — charlietfl, Jul 18 '20 at 16:57

score 3 · Accepted Answer · answered Jul 18 '20 at 17:00

3

It is simply the internal variable of an anonymous function:

m is the parameter variable with value of regex.
m.toUpperCase() is the return value.

Essentially the same as:

function toUpperCase(m){
    return m.toUpperCase();
}

answered Jul 18 '20 at 17:00

Dcdanny

469
2
8

score 2 · Answer 2 · answered Jul 18 '20 at 16:58

In this case m is just a parameter to a function, so a variable name. You can imagine that function written like this:

function toUpperCase(m) {
   return m.toUpperCase();
}

Every match found by your regex will be passed to the function as an argument. The variable m will hold that value.

Arrow function in javascript's replace function

2 Answers2