Reddit Watcher

Consolidated mutation observer handler for use by other reddit userscripts. By itself doesn't do much, but other scripts and use hooks to avoid redundant observers on the same thing.
目前为 2022-03-10 提交的版本。查看最新版本。
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// ==UserScript==
// @name         Reddit Watcher
// @namespace    https://lawrenzo.com/p/reddit-watcher
// @description  Consolidated mutation observer handler for use by other reddit userscripts. By itself doesn't do much, but other scripts and use hooks to avoid redundant observers on the same thing.
// @version      1.3.0
// @author       Lawrence Sim
// @license      WTFPL (http://www.wtfpl.net)
// @grant        unsafeWindow
// @match        *://*.reddit.com/*
// ==/UserScript==
(function() {
    if(unsafeWindow && !unsafeWindow.redditWatcher) {
        var debug = false;
        function watcherAbstract(funcs, opts, name) {
            if(typeof funcs === "function") funcs = {get: funcs};
            return {
                name: name || "unnamed",
                defaultOpts: opts || {childList:true},
                hooks: {
                    update: [],
                    change: []
                },
                onUpdate: function(task) {
                    this.hooks.update.push(task);
                },
                update: function(mutated) {
                    if(debug) console.log(this.name + " updated");
                    this.hooks.update.forEach(task => task(this.watching, mutated));
                },
                onChange: function(task) {
                    this.hooks.change.push(task);
                },
                changed: function() {
                    if(debug) console.log(this.name + " changed");
                    this.hooks.change.forEach(task => task(this.watching));
                },
                un: function(func) {
                    let index = this.hooks.update.indexOf(func);
                    while(~index) {
                        this.hooks.update = this.hooks.splice(index, 1);
                        index = this.hooks.update.indexOf(func);
                    }
                    index = this.hooks.change.indexOf(func);
                    while(~index) {
                        this.hooks.change = this.change.splice(index, 1);
                        index = this.hooks.change.indexOf(func);
                    }
                },
                watching: null,
                watcher: null,
                get: funcs.get,
                reset: function() {
                    if(debug) console.log(this.name + " reset");
                    if(!this.watcher) {
                        this.watcher = new MutationObserver(this.update.bind(this));
                    } else {
                        this.watcher.disconnect();
                    }
                    this.update();
                    this.observe(this.watching, this.defaultOpts);
                },
                observe: function(elem, opts) {
                    if(this.watcher) this.watcher.observe(elem, opts);
                },
                wasChanged: funcs.changed,
                check: function() {
                    if(debug) console.log("checking " + this.name);
                    if(!this.watching || !document.body.contains(this.watching)) {
                        let requery = this.get();
                        if(requery && requery !== this.watching) {
                            this.watching = requery;
                            this.changed();
                            this.reset();
                            return true;
                        }
                    }
                    if(this.wasChanged && this.wasChanged(this.watching)) {
                        this.changed();
                        return true;
                    }
                }
            };
        }
        var lastFirstPost = null,
            feedWatcher = watcherAbstract(
                {
                    get: function() {
                        let listing = document.querySelector(".ListingLayout-outerContainer"),
                            firstPost = listing.querySelector("div[data-testid='post-container']"),
                            feed = firstPost && firstPost.parentNode;
                        while(feed && !feed.nextSibling) {
                            if(feed == listing) return null;
                            feed = feed.parentNode || null;
                        }
                        return feed && feed.parentNode;
                    },
                    changed: function(feed) {
                        let firstPost = feed.querySelector("div[data-testid='post-container']");
                        if(firstPost !== lastFirstPost) {
                            lastFirstPost = firstPost;
                            return true;
                        }
                    }
                },
                {childList:true},
                "feed"
            ),
            listingWatcher = watcherAbstract(
                {get: () => document.querySelector(".ListingLayout-outerContainer")},
                {childList:true, subtree:true},
                "listing"
            ),
            bodyWatcher = watcherAbstract(
                {get: () => document.body},
                {childList:true},
                "body"
            );
        listingWatcher.onChange(() => feedWatcher.check());
        listingWatcher.onUpdate(() => feedWatcher.check());
        var isInFeed = false;
        bodyWatcher.onUpdate(body => {
            if(body.querySelectorAll(".ListingLayout-outerContainer div[data-testid='post-container']").length > 1) {
                isInFeed ? listingWatcher.reset() : listingWatcher.check();
                isInFeed = true;
            } else {
                if(isInFeed) listingWatcher.watcher.disconnect();
                isInFeed = false;
            }
        });
        bodyWatcher.check();
        unsafeWindow.redditWatcher = {
            body:    bodyWatcher,
            listing: listingWatcher,
            feed:    feedWatcher,
            update:  function() { this.body.update(); }
        };
    }
})();
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