纯js压缩图片

备忘

function photoCompress(file, obj, objDiv) {

    var read = new FileReader();

    read.readAsDataURL(file);

    read.onload= function () {

        var result = this.result;

        canvasDataURL(result , obj, objDiv);

    }

};

function canvasDataURL(path, obj, callback) {

    var img = new Image();

    img.src= path;

    img.onload = function () {

        var that = this;

        // 默认按比例压缩

        var wid = that.width/2,

            hei = that.height/2,

            scale = wid/ hei ;

//如果obj有大小，则用obj的大小，否则用默认的

//我这用的长宽压缩一半

        wid = obj.width/2 || wid;

        hei = obj.height/2 || (wid / scale);

        var quality = 0.5; // 默认图片质量为0.7

//生成canvas

        var canvas = document.createElement('canvas');

        var ctx = canvas.getContext('2d');

        // 创建属性节点

        var anw = document.createAttribute("width");

        anw.nodeValue= wid;

        var anh = document.createAttribute("height");

        anh.nodeValue= hei;

        canvas.setAttributeNode(anw);

        canvas.setAttributeNode(anh);

        ctx.drawImage(that, 0, 0, wid, hei);

        // 图像质量

        if (obj.quality&& obj.quality<= 1 && obj.quality> 0) {

            quality = obj.quality;

        }

        // quality值越小，所绘制出的图像越模糊

        var base64 = canvas.toDataURL('image/jpeg', quality);

        // 回调函数返回base64的值

        callback(base64);

    }

}

//base64转blob

function convertBase64UrlToBlob(urlData) {

    var arr = urlData.split(','),

        mime = arr[0].match(/:(.*?);/)[1],

        bstr = atob(arr[1]),

        n = bstr.length,

        u8arr = new Uint8Array(n);

    while (n--) {

        u8arr[n] = bstr.charCodeAt(n);

    }

    return new Blob([u8arr], {

        type: mime

    });

}