ESCMAScript 6 arrow functions - parentheses around parameter

Question

I'm new to javascript and cannot understand simple thing - what is the difference between

(x) => { return x*2}

and

x => { return x*2} //(just for example, may not work)

Can someone explain or give link for description?

Answer 1

The parenthesis around input arguments (x in this case) are only required when there are two or more input arguments. With just one (as you've shown here), the two statements are identical.

(x) => { return x * 2; } is the same as x => { return x * 2; }

But,

(x, y) => { return x * y; }

Requires parenthesis around the input arguments.

See this for all the gory details!