前端压缩图片记录一下

function canvasDataURL(file, callback) {
        //图片压缩  仅支持jpg jpeg bmp图片格式 不支持png 
        var reader = new FileReader()
        reader.readAsDataURL(file)
        reader.onload = function (e) {
            const img = new Image()
            var isLt1M = file.size / 1024 / 1024;
          
            if (isLt1M >= 1) {
                var quality = 0.2// 图像质量
            } else if (isLt1M >= 0.48 && isLt1M < 1) {
                var quality = 0.4 // 图像质量
            } else {
                var quality = 0.7 // 图像质量
            }          
            const canvas = document.createElement('canvas')
            const drawer = canvas.getContext('2d')
            img.src = this.result
            img.onload = function () {
                canvas.width = img.width
                canvas.height = img.height
                drawer.drawImage(img, 0, 0, canvas.width, canvas.height)
                convertBase64UrlToBlob(canvas.toDataURL(file.type, quality), callback);
            }
        }
    }

  function  convertBase64UrlToBlob(urlData, callback) {
        const arr = urlData.split(',')
        const mime = arr[0].match(/:(.*?);/)[1]
        const bstr = atob(arr[1])
        let n = bstr.length
        const u8arr = new Uint8Array(n)
        while (n--) {
            u8arr[n] = bstr.charCodeAt(n)
        }
        callback(new Blob([u8arr], {
            type: mime
        }));
    }
//使用方法
canvasDataURL(file,function (blob) {
    var aafile = new File([blob], file.name, {
        type: file.type
     })
        
})