demonstrating lift

rx js lift.js

import { Observable, Subscriber} from 'rxjs';

const _lift = Observable.prototype.lift;

function LogOperator(childOperator) {
    this.childOperator = childOperator;
}
LogOperator.prototype.call = function (subscriber) {
    return this.childOperator.call(new LogSubscriber(subscriber));
};
window.log = [];
function LogSubscriber() {
    Subscriber.apply(this, arguments);
}
LogSubscriber.prototype = Object.create(Subscriber.prototype);
LogSubscriber.prototype.constructor = LogSubscriber;
LogSubscriber.prototype.next = function (x) {
    log.push('next ' + x);
    this.destination.next(x);
};

Observable.prototype.lift = function(observerFactory) {
    const pretendOperator = {
        call : subscriber => {
            console.log('in call');
            return observerFactory.call(new LogSubscriber(subscriber));
        }
    };
    return _lift.call(this, pretendOperator);
};


window.Observable = Observable;

Observable.of(3).map(val => val*2).subscribe(() => {});

// window.log === ["next 6"]