How to avoid hard coded this? in Decorators

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.

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"

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