关于javascript:图片压缩

如题

const compressImage = async (file, quality=.9) => {    // file 文件对象    // quailty  压缩比        let img = new Image(),        reader = new FileReader(),        canvas = document.createElement('canvas'),        ctx = canvas.getContext('2d')        reader.readAsDataURL(file)    reader.onload = function(e){        img.src = e.target.result    }        return new Promise((resolve, reject)=>{        img.onload = function(){            let _ = this,                w = _.width,                h = _.height,                scale = w / h,                anw = document.createAttribute('width'),                anh = document.createAttribute('height')                            anw.nodeValue = w            anh.nodeValue = h            canvas.setAttribute(anw)            canvas.setAttribute(anh)            // 在canvas绘制前填充红色背景            ctx.rect(0, 0, w, h)            ctx.fillStyle = 'white'            ctx.fill()            ctx.drawImage(_, 0, 0, w, h)            let src = canvas.toDataURL('image/jpeg', quality) //quality 在 'image/jpeg' 时才起作用                        // base64转file            let arr = src.split(','),                bstr = atob(arr[1]),                n = bstr.length,                u8arr = new Uint8Array(8)                while(n--){                    u8arr[n] = bstr.charCodeAt(n)                }                        let newFile = new File([u8arr], file.name, { type: file.type })            console.log('压缩后的图片体积',newFile.size/1024/1024)            resolve(newFile)        }        })    }

里面调用

const egFunc = async (file)=>{    const quality = .5    file = await compressImage(file, quality)}