[CB-3785] Channel.prototype.subscribe to support EventListener interface

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 2.8.0
• Component/s: cordova-js
• Labels: features javascript patch

Environment

All platforms

• Assignee: Ray Shan
• Reporter: Nikolai Kotchetkov
• Created: 13/Jun/13 07:21
• Updated: 23/Aug/18 06:51
• Resolved: 06/Oct/16 23:12

Description

As number of Cordova-specific events use monkey-patch for add/remove/fire listeners it would be nice if Channel functions support EventListener interface:

• https://developer.mozilla.org/en-US/docs/Web/API/EventListener
• http://www.w3.org/TR/DOM-Level-2-Events/events.html#Events-EventListener

I assume only a small patch to Channel module is required. Here are the modified functions to resolve the issue:

/**
 * Subscribes the given function to the channel. Any time that
 * Channel.fire is called so too will the function.
 * Optionally specify an execution context for the function
 * and a guid that can be used to stop subscribing to the channel.
 * Returns the guid.
 */
Channel.prototype.subscribe = function(f, c) {

    var func;
    if (f && "object" === typeof f) {
        // EventListener interface
        func = f["handleEvent"];
        c = f;
    } else {
        // Function interface
        func = f;
    }

    // need a function to call
    forceFunction(func);
    if (this.state == 2) {
        func.apply(c || this, this.fireArgs);
        return;
    }

    var guid = f.observer_guid;
    if (typeof c == "object") { func = utils.close(c, func); }

    if (!guid) {
        // first time any channel has seen this subscriber
        guid = '' + nextGuid++;
    }
    func.observer_guid = guid;
    f.observer_guid = guid;

    // Don't add the same handler more than once.
    if (!this.handlers[guid]) {
        this.handlers[guid] = func;
        this.numHandlers++;
        if (this.numHandlers == 1) {
            this.onHasSubscribersChange && this.onHasSubscribersChange();
        }
    }
};

/**
 * Unsubscribes the function with the given guid from the channel.
 */
Channel.prototype.unsubscribe = function(f) {
    var func;
    if (f && "object" === typeof f) {
        // EventListener interface
        func = f["handleEvent"];
        c = f;
    } else {
        // Function interface
        func = f;
    }

    // need a function to unsubscribe
    forceFunction(func);

    var guid = f.observer_guid,
        handler = this.handlers[guid];
    if (handler) {
        delete this.handlers[guid];
        this.numHandlers--;
        if (this.numHandlers === 0) {
            this.onHasSubscribersChange && this.onHasSubscribersChange();
        }
    }
};

Issue Links

• is blocked by: CB-3786 Event's 'target' and 'currentTarget' are null for monkeypatched events
• links to: GitHub Pull Request #130