H5的FileReader怎样分布读取文件-木庄网络博客

本文摘自PHP中文网，作者php中世界最好的语言，侵删。

这次给大家带来H5的FileReader怎样分布读取文件，FileReader分布读取文件的注意事项有哪些，下面就是实战案例，一起来看一下。

效果图

老规矩先上效果图

先介绍一下H5中FileReader的一些方法以及事件

FileReader方法

名称	作用
about()	终止读取
readAsBinaryString(file)	将文件读取为二进制编码
readAsDataURL(file)	将文件读取为DataURL编码
readAsText(file, [encoding])	将文件读取为文本
readAsArrayBuffer(file)	将文件读取为arraybuffer

FileReader事件

名称	作用
onloadstart	读取开始时触发
onprogress	读取中
onloadend	读取完成触发，无论成功或失败
onload	文件读取成功完成时触发
onabort	中断时触发
onerror	出错时触发

代码

分布读取文件核心思想, 将文件分块以每M进行读取.

HTML部分

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Document</title>
</head>
<body>
    <form>
        <fieldset>
            <legend>分步读取文件：</legend>
            <input type="file" id="File">
            <input type="button" value="中断" id="Abort">
            <p>
                <lable>读取进度：</lable>
                <progress id="Progress" value="0" max="100"></progress>
            </p>
        </fieldset>
    </form>
    <script src="./loadFile.js"></script>
    <script>
            var progress = document.getElementById('Progress');//进度条
            var events = {
                load: function () {
                    console.log('loaded');
                },
                progress: function (percent) {
                    console.log(percent);
                    progress.value = percent;
                },
                success: function () {
                    console.log('success');
                }
            };
            var loader;
            // 选择好要上传的文件后触发onchange事件
            document.getElementById('File').onchange = function (e) {
                var file = this.files[0];
                console.log(file)
                //loadFile.js
                loader = new FileLoader(file, events);
            };
            document.getElementById('Abort').onclick = function () {
                loader.abort();
            }
        </script>
</body>
</html>

loadFile.js部分

/*
* 文件读取模块
* file  文件对象
* events 事件回掉对象 包含 success , load, progress
*/
var FileLoader = function (file, events) {
    this.reader = new FileReader();
    this.file = file;
    this.loaded = 0;
    this.total = file.size;
    //每次读取1M
    this.step = 1024 * 1024;
    this.events = events || {};
    //读取第一块
    this.readBlob(0);
    this.bindEvent();  
}
FileLoader.prototype = {
    bindEvent: function (events) {
        var _this = this,
            reader = this.reader;
        reader.onload = function (e) {
            _this.onLoad();
        };
        reader.onprogress = function (e) {
            _this.onProgress(e.loaded);
        };
        // start 、abort、error 回调暂时不加
    },
    // progress 事件回掉
    onProgress: function (loaded) {
        var percent,
            handler = this.events.progress;//进度条
        this.loaded += loaded;
        percent = (this.loaded / this.total) * 100;
        handler && handler(percent);
    },
    // 读取结束（每一次执行read结束时调用，并非整体）
    onLoad: function () {
        var handler = this.events.load;
        // 应该在这里发送读取的数据
        handler && handler(this.reader.result);
        // 如果未读取完毕继续读取
        if (this.loaded < this.total) {
            this.readBlob(this.loaded);
        } else {
            // 读取完毕
            this.loaded = this.total;
            // 如果有success回掉则执行
            this.events.success && this.events.success();
        }
    },
    // 读取文件内容
    readBlob: function (start) {
        var blob,
            file = this.file;
        // 如果支持 slice 方法，那么分步读取，不支持的话一次读取
        if (file.slice) {
            blob = file.slice(start, start + this.step);
        } else {
            blob = file;
        }
        this.reader.readAsText(blob);
    },
    // 中止读取
    abort: function () {
        var reader = this.reader;
        if(reader) {
            reader.abort();
        }
    }
}