技術(shù)要點

• FileReader去讀取圖片
• 使用canvas的API去壓縮
• buffer處理后上傳

HTML

<input type="file" id="choose" accept="image/*" multiple>
<ul class="img-list"></ul>
<a id="upload">上傳圖片</a>
<span class="tips">只允許上傳jpg纷宇、png及gif</span>
<div class="pic-list">
    你上傳的圖片(圖片有效期為1分鐘)：
</div>

JS(使用jQuery庫)

var filechooser = document.getElementById("choose");
//    用于壓縮圖片的canvas
var canvas = document.createElement("canvas");
var ctx = canvas.getContext('2d');
//    瓦片canvas
var tCanvas = document.createElement("canvas");
var tctx = tCanvas.getContext("2d");
var maxsize = 100 * 1024;//自定義只對超過100kb的圖片進(jìn)行壓縮
$("#upload").on("click", function() {
        filechooser.click();
    })
filechooser.onchange = function() {
        if (!this.files.length) return;
        var files = Array.prototype.slice.call(this.files);
        if (files.length > 9) {
            alert("最多同時只可上傳9張圖片");
            return;
        }
        files.forEach(function(file, i) {
            if (!/\/(?:jpeg|png|gif)/i.test(file.type)) return;
            var reader = new FileReader();
            var li = document.createElement("li");
//          獲取圖片大小
            var size = file.size / 1024 > 1024 ? (~~(10 * file.size / 1024 / 1024)) / 10 + "MB" : ~~(file.size / 1024) + "KB";
            li.innerHTML = '<div class="progress"><span></span></div><div class="size">' + size + '</div>';
            $(".img-list").append($(li));
            // 讀取圖片后觸發(fā)
            reader.onload = function() {
                var result = this.result;
                var img = new Image();
                img.src = result;
                $(li).css("background-image", "url(" + result + ")");
                //如果圖片大小小于100kb寄悯，則直接上傳
                if (result.length <= maxsize) {
                    img = null;
                    upload(result, file.type, $(li));
                    return;
                }
//      圖片加載完畢之后進(jìn)行壓縮灌闺，然后上傳
                if (img.complete) {
                    callback();
                } else {
                    // 瀏覽器顯示原圖后觸發(fā)callback進(jìn)行壓縮上傳
                    img.onload = callback;
                }
                function callback() {
                    var data = compress(img);
                    upload(data, file.type, $(li));
                    img = null;
                }
            };
           // 去讀取選擇的文件到內(nèi)存
            reader.readAsDataURL(file);
        })
    };
    //    使用canvas對大圖片進(jìn)行壓縮
    function compress(img) {
        var initSize = img.src.length;
        var width = img.width;
        var height = img.height;
        //如果圖片大于四百萬像素，計算壓縮比并將大小壓至400萬以下
        var ratio;
        if ((ratio = width * height / 4000000) > 1) {
            ratio = Math.sqrt(ratio);
            width /= ratio;
            height /= ratio;
        } else {
            ratio = 1;
        }
        canvas.width = width;
        canvas.height = height;
//        鋪底色
        ctx.fillStyle = "#fff";
        ctx.fillRect(0, 0, canvas.width, canvas.height);
        //如果圖片像素大于100萬則使用瓦片繪制
        var count;
        if ((count = width * height / 1000000) > 1) {
            // ~~ 的作用類似于Math.floor(),性能會好一點
            count = ~~(Math.sqrt(count) + 1); //計算要分成多少塊瓦片
//            計算每塊瓦片的寬和高
            var nw = ~~(width / count);
            var nh = ~~(height / count);
            tCanvas.width = nw;
            tCanvas.height = nh;
           // 先畫一個小的tctx坏瞄，然后將小的從左到右菩鲜，從上到下畫到大的ctx畫布上
            for (var i = 0; i < count; i++) {
                for (var j = 0; j < count; j++) {
                    tctx.drawImage(img, i * nw * ratio, j * nh * ratio, nw * ratio, nh * ratio, 0, 0, nw, nh);
                    ctx.drawImage(tCanvas, i * nw, j * nh, nw, nh);
                }
            }
        } else {
            ctx.drawImage(img, 0, 0, width, height);
        }
        //進(jìn)行最小壓縮（真正壓縮的api）
        var ndata = canvas.toDataURL('image/jpeg', 0.1);
        console.log('壓縮前：' + initSize);
        console.log('壓縮后：' + ndata.length);
        console.log('壓縮率：' + ~~(100 * (initSize - ndata.length) / initSize) + "%");
        tCanvas.width = tCanvas.height = canvas.width = canvas.height = 0;
        return ndata;
    }
    //    圖片上傳，將base64的圖片轉(zhuǎn)成二進(jìn)制對象惦积，塞進(jìn)formdata上傳
    function upload(basestr, type, $li) {
       // 截取圖片base64的數(shù)據(jù)然后轉(zhuǎn)為二進(jìn)制數(shù)據(jù)接校，atob與btoa是一對api
        var text = window.atob(basestr.split(",")[1]);
        // Uint8Array: 對象 8 位無符號整數(shù)值的類型化數(shù)組。內(nèi)容將初始化為 0
        var buffer = new Uint8Array(text.length);
        var pecent = 0, loop = null;
        for (var i = 0; i < text.length; i++) {
            buffer[i] = text.charCodeAt(i);
        }
        var blob = getBlob([buffer], type);
        var xhr = new XMLHttpRequest();
       // 新建表單對象
        var formdata = getFormData();
        formdata.append('file', blob);
        formdata.append('desc', 'compress_upload');
        formdata.append('tel', 'tel');

        xhr.open('post', '/upload_compress');
        xhr.onreadystatechange = function() {
            if (xhr.readyState == 4 && xhr.status == 200) {
                console.log(xhr);

                var jsonData = JSON.parse(xhr.responseText);
                var imagedata = jsonData[0] || {};
                var text = imagedata.path ? '上傳成功' : '上傳失敗';
                console.log(text + '：' + imagedata.path);
                clearInterval(loop);
                //當(dāng)收到該消息時上傳完畢
                $li.find(".progress span").animate({'width': "100%"}, pecent < 95 ? 200 : 0, function() {
                    $(this).html(text);
                });
                if (!imagedata.path) return;
                $(".pic-list").append('<a href="' + imagedata.path + '">' + imagedata.name + '（' + imagedata.size + '）![](' + imagedata.path + ')</a>');
            }
        };
        //數(shù)據(jù)發(fā)送進(jìn)度狮崩，前50%展示該進(jìn)度
        xhr.upload.addEventListener('progress', function(e) {
            if (loop) return;
            pecent = ~~(100 * e.loaded / e.total) / 2;
            $li.find(".progress span").css('width', pecent + "%");
            if (pecent == 50) {
                mockProgress();
            }
        }, false);
        //數(shù)據(jù)后50%用模擬進(jìn)度
        function mockProgress() {
            if (loop) return;
            loop = setInterval(function() {
                pecent++;
                $li.find(".progress span").css('width', pecent + "%");
                if (pecent == 99) {
                    clearInterval(loop);
                }
            }, 100)
        }
        // 上傳
        xhr.send(formdata);
    }

    /**
     * 獲取blob對象的兼容性寫法
     * @param  {string} buffer 文件內(nèi)容
     * @param  {string} format 文件類別
     * @return {Blob}        二進(jìn)制文件的容器
     */
    function getBlob(buffer, format) {
        try {
            return new Blob(buffer, {type: format});
        } catch (e) {
            var bb = new (window.BlobBuilder || window.WebKitBlobBuilder || window.MSBlobBuilder);
            buffer.forEach(function(buf) {
                bb.append(buf);
            });
            return bb.getBlob(format);
        }
    }
    /**
     * 獲取formdata
     */
    function getFormData() {
       // 檢測瀏覽器
        var isNeedShim = ~navigator.userAgent.indexOf('Android')
            && ~navigator.vendor.indexOf('Google')
            && !~navigator.userAgent.indexOf('Chrome')
            && navigator.userAgent.match(/AppleWebKit\/(\d+)/).pop() <= 534;
        return isNeedShim ? new FormDataShim() : new FormData()
    }
    /**
     * formdata 補(bǔ)丁, 給不支持formdata上傳blob的android機(jī)打補(bǔ)丁
     * @constructor
     */
    function FormDataShim() {
        console.warn('using formdata shim');
        var o = this,
            parts = [],
            boundary = Array(21).join('-') + (+new Date() * (1e16 * Math.random())).toString(36),
            oldSend = XMLHttpRequest.prototype.send;
        this.append = function(name, value, filename) {
            parts.push('--' + boundary + '\r\nContent-Disposition: form-data; name="' + name + '"');
            if (value instanceof Blob) {
                parts.push('; filename="' + (filename || 'blob') + '"\r\nContent-Type: ' + value.type + '\r\n\r\n');
                parts.push(value);
            }
            else {
                parts.push('\r\n\r\n' + value);
            }
            parts.push('\r\n');
        };
        // Override XHR send()
        XMLHttpRequest.prototype.send = function(val) {
            var fr,
                data,
                oXHR = this;
            if (val === o) {
                // Append the final boundary string
                parts.push('--' + boundary + '--\r\n');
                // Create the blob
                data = getBlob(parts);
                // Set up and read the blob into an array to be sent
                fr = new FileReader();
                fr.onload = function() {
                    oldSend.call(oXHR, fr.result);
                };
                fr.onerror = function(err) {
                    throw err;
                };
                fr.readAsArrayBuffer(data);
                // Set the multipart content type and boudary
                this.setRequestHeader('Content-Type', 'multipart/form-data; boundary=' + boundary);
                XMLHttpRequest.prototype.send = oldSend;
            }
            else {
                oldSend.call(this, val);
            }
        };
    }

done

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