这是一个异步获取元素的脚本库。不少人写脚本都碰到过元素延迟加载的问题，使用定时器获取不仅实时性不足，还有性能问题，DOMNodeInserted的性能也不好，一般都推荐MutationObserver的方案。但是MutationObserver的语法较复杂，回调函数的写法也不易于使用，因此本库将相关代码加以封装，让元素获取一步到位，方便脚本的快速开发。
Dit script moet niet direct worden geïnstalleerd - het is een bibliotheek voor andere scripts om op te nemen met de meta-richtlijn // @require https://update.greasyfork.org/scripts/477884/1267853/ElementGetter_gf.js
// ==UserScript==
// @name ElementGetter_gf
// @author cxxjackie
// @version 2.0.0
// @supportURL https://bbs.tampermonkey.net.cn/thread-2726-1-1.html
// ==/UserScript==
var elmGetter = function() {
const win = window.unsafeWindow || document.defaultView || window;
const doc = win.document;
const listeners = new WeakMap();
let mode = 'css';
let $;
const elProto = win.Element.prototype;
const matches = elProto.matches ||
elProto.matchesSelector ||
elProto.webkitMatchesSelector ||
elProto.mozMatchesSelector ||
elProto.oMatchesSelector;
const MutationObs = win.MutationObserver ||
win.WebkitMutationObserver ||
win.MozMutationObserver;
function addObserver(target, callback) {
const observer = new MutationObs(mutations => {
for (const mutation of mutations) {
if (mutation.type === 'attributes') {
callback(mutation.target);
if (observer.canceled) return;
}
for (const node of mutation.addedNodes) {
if (node instanceof Element) callback(node);
if (observer.canceled) return;
}
}
});
observer.canceled = false;
observer.observe(target, {childList: true, subtree: true, attributes: true});
return () => {
observer.canceled = true;
observer.disconnect();
};
}
function addFilter(target, filter) {
let listener = listeners.get(target);
if (!listener) {
listener = {
filters: new Set(),
remove: addObserver(target, el => listener.filters.forEach(f => f(el)))
};
listeners.set(target, listener);
}
listener.filters.add(filter);
}
function removeFilter(target, filter) {
const listener = listeners.get(target);
if (!listener) return;
listener.filters.delete(filter);
if (!listener.filters.size) {
listener.remove();
listeners.delete(target);
}
}
function query(all, selector, parent, includeParent, curMode) {
switch (curMode) {
case 'css':
const checkParent = includeParent && matches.call(parent, selector);
if (all) {
const queryAll = parent.querySelectorAll(selector);
return checkParent ? [parent, ...queryAll] : [...queryAll];
}
return checkParent ? parent : parent.querySelector(selector);
case 'jquery':
let jNodes = $(includeParent ? parent : []);
jNodes = jNodes.add([...parent.querySelectorAll('*')]).filter(selector);
if (all) return $.map(jNodes, el => $(el));
return jNodes.length ? $(jNodes.get(0)) : null;
case 'xpath':
const ownerDoc = parent.ownerDocument || parent;
selector += '/self::*';
if (all) {
const xPathResult = ownerDoc.evaluate(selector, parent, null, 7, null);
const result = [];
for (let i = 0; i < xPathResult.snapshotLength; i++) {
result.push(xPathResult.snapshotItem(i));
}
return result;
}
return ownerDoc.evaluate(selector, parent, null, 9, null).singleNodeValue;
}
}
function isJquery(jq) {
return jq && jq.fn && typeof jq.fn.jquery === 'string';
}
function getOne(selector, parent, timeout) {
const curMode = mode;
return new Promise(resolve => {
const node = query(false, selector, parent, false, curMode);
if (node) return resolve(node);
let timer;
const filter = el => {
const node = query(false, selector, el, true, curMode);
if (node) {
removeFilter(parent, filter);
timer && clearTimeout(timer);
resolve(node);
}
};
addFilter(parent, filter);
if (timeout > 0) {
timer = setTimeout(() => {
removeFilter(parent, filter);
resolve(null);
}, timeout);
}
});
}
return {
get currentSelector() {
return mode;
},
get(selector, ...args) {
let parent = typeof args[0] !== 'number' && args.shift() || doc;
if (mode === 'jquery' && parent instanceof $) parent = parent.get(0);
const timeout = args[0] || 0;
if (Array.isArray(selector)) {
return Promise.all(selector.map(s => getOne(s, parent, timeout)));
}
return getOne(selector, parent, timeout);
},
each(selector, ...args) {
let parent = typeof args[0] !== 'function' && args.shift() || doc;
if (mode === 'jquery' && parent instanceof $) parent = parent.get(0);
const callback = args[0];
const curMode = mode;
const refs = new WeakSet();
for (const node of query(true, selector, parent, false, curMode)) {
refs.add(curMode === 'jquery' ? node.get(0) : node);
if (callback(node, false) === false) return;
}
const filter = el => {
for (const node of query(true, selector, el, true, curMode)) {
const _el = curMode === 'jquery' ? node.get(0) : node;
if (refs.has(_el)) break;
refs.add(_el);
if (callback(node, true) === false) {
return removeFilter(parent, filter);
}
}
};
addFilter(parent, filter);
},
create(domString, ...args) {
const returnList = typeof args[0] === 'boolean' && args.shift();
const parent = args[0];
const template = doc.createElement('template');
template.innerHTML = domString;
const node = template.content.firstElementChild;
if (!node) return null;
parent ? parent.appendChild(node) : node.remove();
if (returnList) {
const list = {};
node.querySelectorAll('[id]').forEach(el => list[el.id] = el);
list[0] = node;
return list;
}
return node;
},
selector(desc) {
switch (true) {
case isJquery(desc):
$ = desc;
return mode = 'jquery';
case !desc || typeof desc.toLowerCase !== 'function':
return mode = 'css';
case desc.toLowerCase() === 'jquery':
for (const jq of [window.jQuery, window.$, win.jQuery, win.$]) {
if (isJquery(jq)) {
$ = jq;
break;
};
}
return mode = $ ? 'jquery' : 'css';
case desc.toLowerCase() === 'xpath':
return mode = 'xpath';
default:
return mode = 'css';
}
}
};
}();