How to avoid hard coded this? in Decorators

Question

I have read \"How to implement a typescript decorator?\" and multiple sources but there is something that i have nor been able to do with decorators.

class F         


        

Answer 1

Don't use an arrow function. Use a function expression:

function log(target: Object, key: string, value: any) {
    return {
        value: function(...args: any[]) {
            var a = args.map(a => JSON.stringify(a)).join();
            var result = value.value.apply(this, args);
            var r = JSON.stringify(result);
            console.log(`Call: ${key}(${a}) => ${r}`);
            return result;
        }
    };
}

That way it will use the function's this context instead of the value of this when log is called.

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By the way, I would recommend editing the descriptor/value parameter and return that instead of overwriting it by returning a new descriptor. That way you keep the properties currently in the descriptor and won't overwrite what another decorator might have done to the descriptor:

function log(target: Object, key: string, descriptor: TypedPropertyDescriptor<any>) {
    var originalMethod = descriptor.value;

    descriptor.value = function(...args: any[]) {
        var a = args.map(a => JSON.stringify(a)).join();
        var result = originalMethod.apply(this, args);
        var r = JSON.stringify(result);
        console.log(`Call: ${key}(${a}) => ${r}`);
        return result;
    };

    return descriptor;
}

More details in this answer - See the "Bad vs Good" example under "Example - Without Arguments > Notes"

Answer 2

I believe you can use

var self = this;

in order to preserve the 'this' at that specific point. Then, just use self at the later point where you would have wanted that particular this