TypeScript lambda functions with additional parameters

Question

I'm having problems defining a lambda function that takes an optional parameter. The strange part is that if I use the full syntax of the “function”, the anonymous function works, but the lambda shortcut / arrow syntax causes errors like the following:

• The name 'a' does not exist in the current scope
• The supplied parameters do not match any target call signature
• Expected ')'

Example:

(function (a, b?) => { console.log(a, b); })("a"); // OK ((a, b?) => { console.log(a, b); })("a", "b"); // Errors ((a, b) => { console.log(a, b); })("a", "b"); // OK 

Answer 1

This is a compiler error and is being fixed right now [v0.8]. Lambdas currently provides error messages with options and rest options. Please use long function syntax if this is a lock problem.

Answer 2

There is currently an error with optional parameter annotation in fat lambda expressions arrow.