在网页中实现图片上传功能,当用户选择了图片文件后,想在页面中即时预览该图片,这个简单的需求在很久很久以前可以实现,后来因为安全性的问题被禁止直接访问本地文件了,所以又在很长很长一段时间里,想通过HTML直接预览用户选择的图片变得不可能,自从有了HTML5,这个功能又回来了,通过FileReader可以轻松的实现这个功能。
只要在3e701519c4bde102649c97eab49f5c17文件表单元素中监听 onchange
事件,然后通过FileReader读取图片文件,然后将读取的内容在中显示即可。示例代码如下:
document.getElementById('file').onchange = function(evt) { // 如果浏览器不支持FileReader,则不处理 if (window.FileReader) return ; var files = evt.target.files; for (var i = 0, f; f = files[i]; i++) { if (!f.type.match('image.*')) { continue ; } var reader = new FileReader(); reader.onload = (function(theFile) { return function(e) { // img 元素 document.getElementById('previewImage').src = e.target.result; }; })(f); reader.readAsDataURL(f); } }
以上就是用HTML5轻松实现图片预览的内容,更多相关内容请关注PHP中文网(www.php.cn)!
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Web standards and technologies have evolved from HTML4, CSS2 and simple JavaScript to date and have undergone significant developments. 1) HTML5 introduces APIs such as Canvas and WebStorage, which enhances the complexity and interactivity of web applications. 2) CSS3 adds animation and transition functions to make the page more effective. 3) JavaScript improves development efficiency and code readability through modern syntax of Node.js and ES6, such as arrow functions and classes. These changes have promoted the development of performance optimization and best practices of web applications.

H5 is not just the abbreviation of HTML5, it represents a wider modern web development technology ecosystem: 1. H5 includes HTML5, CSS3, JavaScript and related APIs and technologies; 2. It provides a richer, interactive and smooth user experience, and can run seamlessly on multiple devices; 3. Using the H5 technology stack, you can create responsive web pages and complex interactive functions.

H5 and HTML5 refer to the same thing, namely HTML5. HTML5 is the fifth version of HTML, bringing new features such as semantic tags, multimedia support, canvas and graphics, offline storage and local storage, improving the expressiveness and interactivity of web pages.

H5referstoHTML5,apivotaltechnologyinwebdevelopment.1)HTML5introducesnewelementsandAPIsforrich,dynamicwebapplications.2)Itsupportsmultimediawithoutplugins,enhancinguserexperienceacrossdevices.3)SemanticelementsimprovecontentstructureandSEO.4)H5'srespo

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