error "Invalid parenthesized assignment pattern" background info

Question

In my React project, I got this error:

SyntaxError: ... Invalid parenthesized assignment pattern
const add = (a, b) = { return a + b; };
             ^

I do understand the error, but I am surprised that I could not find any information about it.

• Where does it come from ?
• Where is it documented ?

What I want to understand

I do understand the problem here (the '>' is missing in this arrow function), but I wonder (1) where this error comes from exactly (not the Browser?), and (2) where could I find information about it.

The error message obviously interprets this as a wrong assignment, not as a wrong arrow function:

const add = (a, b) = { return a + b; };
// error ----^
// actually wrong --^

Where it obviously does not come from:

If I write the same statement in the NodeJs CLI, I get:

const add = (a,b) = { return ''; }
            ^^^^^
ReferenceError: Invalid left-hand side in assignment

in the Firefox console:

SyntaxError: invalid assignment left-hand side

Note that I am using Firefox for development, but the error message during development is different than the error message when I try the same in the Firefox console (Invalid parenthesized assignment pattern vs. SyntaxError: invalid assignment left-hand side)

Answer 1

Since you are using the ES6 arrow function, you have to define =>

const add = (a, b) = { return a + b; }; // here you missed arrow for function **=>**

const add = (a, b) **=>** { return a + b; }; //modified by adding **=>**