@cycle/dom/lib/es6/fromEvent.js

The standard DOM Driver for Cycle.js, based on Snabbdom

import { Stream } from 'xstream';
export function fromEvent(element, eventName, useCapture, preventDefault, passive) {
    if (useCapture === void 0) { useCapture = false; }
    if (preventDefault === void 0) { preventDefault = false; }
    if (passive === void 0) { passive = false; }
    var next = null;
    return Stream.create({
        start: function start(listener) {
            if (preventDefault) {
                next = function _next(event) {
                    preventDefaultConditional(event, preventDefault);
                    listener.next(event);
                };
            }
            else {
                next = function _next(event) {
                    listener.next(event);
                };
            }
            element.addEventListener(eventName, next, {
                capture: useCapture,
                passive: passive,
            });
        },
        stop: function stop() {
            element.removeEventListener(eventName, next, useCapture);
            next = null;
        },
    });
}
function matchObject(matcher, obj) {
    var keys = Object.keys(matcher);
    var n = keys.length;
    for (var i = 0; i < n; i++) {
        var k = keys[i];
        if (typeof matcher[k] === 'object' && typeof obj[k] === 'object') {
            if (!matchObject(matcher[k], obj[k])) {
                return false;
            }
        }
        else if (matcher[k] !== obj[k]) {
            return false;
        }
    }
    return true;
}
export function preventDefaultConditional(event, preventDefault) {
    if (preventDefault) {
        if (typeof preventDefault === 'boolean') {
            event.preventDefault();
        }
        else if (isPredicate(preventDefault)) {
            if (preventDefault(event)) {
                event.preventDefault();
            }
        }
        else if (typeof preventDefault === 'object') {
            if (matchObject(preventDefault, event)) {
                event.preventDefault();
            }
        }
        else {
            throw new Error('preventDefault has to be either a boolean, predicate function or object');
        }
    }
}
function isPredicate(fn) {
    return typeof fn === 'function';
}
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