dom

问题 I can't fully understand how Object.defineProperty works on dom elements. On normal javascript objects it works like a charm var obj={name: 'john'}; Object.defineProperty(obj, 'name', { get: function(){ console.log('get value') }, set:function(newValue){ console.log('set value '+newValue); }, configurable: true }); the line obj.name='Tom'; will print to console 'set value Tom' and change obj.name to Tom. When I try it on a dom element (e.g. on the property checked of a checkbox), it will

问题 I have a reference to an element that will at some point be upgraded to a custom element. How do I wait for it to be upgraded? For example, suppose el is the reference. If it hypothetically had a promise attached to it for this purpose, code could be similar to await el.upgradePromise // do something after it has been upgraded. That of course doesn't exist, but describes what I want to do. Maybe there is no way to do it without polling? If I use polling, what would I poll for (suppose I don't

问题 I have a reference to an element that will at some point be upgraded to a custom element. How do I wait for it to be upgraded? For example, suppose el is the reference. If it hypothetically had a promise attached to it for this purpose, code could be similar to await el.upgradePromise // do something after it has been upgraded. That of course doesn't exist, but describes what I want to do. Maybe there is no way to do it without polling? If I use polling, what would I poll for (suppose I don't

问题 The DOM NodeList (as returned e.g. by element.getElementsByTagName) is an interesting object, in that it is not a snapshot, but reflects changes to the document made after you have created the NodeList. I was wondering how one would implement such a collection: Completely lazy evaluation must be horribly slow, but keeping a cached version consistent requires a lot of book-keeping internally. I tried to google for blog articles on the subject, and also tried to find the relevant source code

问题 The DOM NodeList (as returned e.g. by element.getElementsByTagName) is an interesting object, in that it is not a snapshot, but reflects changes to the document made after you have created the NodeList. I was wondering how one would implement such a collection: Completely lazy evaluation must be horribly slow, but keeping a cached version consistent requires a lot of book-keeping internally. I tried to google for blog articles on the subject, and also tried to find the relevant source code

问题 I am unable to import org.w3c.dom.NodeList package to Eclipse. It is showing The package org.w3c.dom is accessible from more than one module: <unnamed> , java.xml" error message in eclipse. Please let me know how to fix this ? Eclipse Version: Eclipse IDE for Enterprise Java Developers. Version: 2019-06 (4.12.0) Build id: 20190614-1200 Java version: java version "12.0.1" 2019-04-16 Java(TM) SE Runtime Environment (build 12.0.1+12) Java HotSpot(TM) 64-Bit Server VM (build 12.0.1+12, mixed mode

问题 I have in my html document several div elements with certain css class and want to get x, y position of those elements, thanks in advance. 回答1: Use getBoundingClientRect : http://ejohn.org/blog/getboundingclientrect-is-awesome/ For example: var div = document.getElementById("yourDiv"); var rect = div.getBoundingClientRect(); alert("Coordinates: " + rect.left + "px, " + rect.top + "px"); Remember that getBoundingClientRect gives the coordinates relative to the current viewport , which means

问题 I’m trying to get the value property from my <input> field so I can later use it to fetch data from a specific API URL. The problem is that my <input> value is always empty no matter what I type in it. I tried to use document.querySelector() and document.getElementById() ; both yield the same result. const searchBtn = document.querySelector("#searchBtn"); //const inpuValue = document.querySelector("#inputField").value; const inputValue = (document.getElementById("inputField")).value; const

问题 Given a textarea with content that flows like this –––––––––––––––––––––––––– | This is some text, which | | wraps like this. | –––––––––––––––––––––––––– How can one tell if the text-cursor is on the first line of the textarea? Obviously, checking for a newline character ( \n ) works if one wants to see if the cursor appears before the first line break, but testing for a 'soft' line break seems more challenging. Here is a sample jsFiddle to experiment with. I have not yet come up with a

问题 Sometimes I need to get elements like this: var object = document.getElementById('ObjectName'); And sometimes like this: var object = document.getElementById('#ObjectName'); What’s the difference between them? 回答1: No, you don't see var object = document.getElementById('#ObjectName'); You don't see that because that would mean the id of the element starts with # and HTML4 id could only start "with a letter ([A-Za-z])". What you see is sometimes people using the jQuery library in which the