ES6 immediately invoked arrow function

Question

Why does this work in a Node.js console (tested in 4.1.1 and 5.3.0) but doesn\'t work in the browser (tested in Chrome)? This code block should create and invok

Answer 1

None of these should work without parentheses.

Why?

Because according in the spec:

1. ArrowFunction is listed under AssignmentExpression
2. The LHS of a CallExpression must be a MemberExpression, SuperCall or CallExpression

So an ArrowFunction cannot be on the LHS of a CallExpression.

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What this effectively means in how => should be interpreted, is that it works on the same sort of level as assignment operators =, += etc.

Meaning

• x => {foo}() doesn't become (x => {foo})()
• The interpreter tries to interpret it as x => ({foo}())
• Thus it's still a SyntaxError
• So the interpreter decides that the ( must have been wrong and throws a SyntaxError

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There was a bug on Babel about it here, too.