其实判断一个元素是否存在,用getElementById()(或其他选择元素的方法)再配合是否为null来判断,或用jQuery获取对象并判断其length,简单又直接。 但如果想判断一个元素是否在当前实时可见的dom中,那就用node.contains(othernode)方法。 参考: 1,How to check if element exists in the visi
JavaScript—Element元素对象 Element元素 上一篇介绍了Element对象,Element对象表示HTML里的元素。Element 对象可以拥有类型为元素节点、文本节点、注释节点的子节点,所谓的节点就是一个个的标签元素,Document 对象可以得到Element 对象,可通过 document .Element 对其进行访问。 然后也介绍了相关的属性和方法,常见的属性和方...
Let's suppose we have the following HTML element: <div id="example"class="foo-bar baz"></div> To check whether a certain class exists on the element, we can use any of the following methods: #UsingElement.classList.contains()
首先,获取到iframe元素的引用。可以使用document.getElementById()或其他选择器方法来获取iframe元素的引用。例如,如果iframe元素的id为"myIframe",可以使用以下代码获取到该元素的引用: 代码语言:txt 复制 var iframe = document.getElementById("myIframe"); ...
由于Html代码是从上到下执行,如果Head中的js代码耗时严重,就会导致用户长时间无法看到页面,如果放置在body代码块底部,那么即使js代码耗时严重,也不会影响用户看到页面效果,只是js实现特效慢而已。 <!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> ...
indexOf(4).should.equal(-1); }); }); context('when present', function() { it('should return the index where the element first appears in the array', function() { [1, 2, 3].indexOf(3).should.equal(2); }); }); }); }); ...
By creating an element and then converting it to a string representation we can match against “[object HTMLUnknownElement]” to check whether an element has been registered to customElements or exists by default. function validHTML(element) { return document.createElement(element.toUpperCase())....
WinJS.Utilities.markSupportedForProcessing (window.errorLogger =function(sender, evt){ adEvents.innerHTML = (newDate()).toLocaleTimeString() +": "+ sender.element.id +" error: "+ evt.errorMessage +" error code: "+ evt.errorCode +"<br>"+ adEvents.innerHTML; } ); ...
JavaScript has a hasAttribute() function which can be used to test whether an attribute exists on an element or not. It returns a boolean true if a match is found and a boolean false when no match is found. For example: // usage 1: using pure JavaScript document.getElementById('...
The most commonly used DOM method is getElementById. It takes one parameter: a case-sensitive string with the element’s identifier. It returns an element object, which is referenced to the element if it exists; otherwise, it returns null. The returned element object has a set of methods ...