TypeScript: Decorators for Function Expressions

Question

I am trying to add a function decorator to a function expression. The decorator works for function declarations but not for function expressions.

Decorator:

function track(val: string) {

    return function(_target: any, _key: string, descriptor: any)  {

        const originalMethod = descriptor.value;

        descriptor.value = function(...args: any[]) {
           Logger.log(val);
           originalMethod.apply(this, args);
        };

        return descriptor;
    };

Function expression which I'm trying to annotate: It will not work if I try to decorate like this:

const handleClick = @track('trackMe') (e) => { console.log(e) };

or this:

@trackMetric('sdf')
const handleClick = (e) => { console.log(e) };

I have experimentalDecorators flag on and targets ES5.

Answer 1

You can not decorate a function, you can ONLY decorate:

• Class constructors
• Class methods
• Class method parameters
• Class getters/setters
• Class properties