exif.js解决ios手机上传竖拍照片旋转90度问题

// ios手机图片被翻转处理
import EXIF from 'exif-js'

// file为Blob对象
function transformImg(file) {
    let Orientation = null
    return new Promise((resolve => {
        EXIF.getData(file, function () {
            EXIF.getAllTags(this)
            Orientation = EXIF.getTag(this, 'Orientation')
            if (Orientation && Orientation != 1) { // 图片角度不正确
                let canvas = document.createElement("canvas")
                let ctx = canvas.getContext('2d')
                let img = new Image()
                img.src = window.URL.createObjectURL(file)
                img.onload = function () {
                    let imgHeight = this.height
                    let imgWidth = this.width
                    switch (Orientation) {
                        case 6: // 旋转90度
                            canvas.width = imgHeight
                            canvas.height = imgWidth
                            ctx.rotate(Math.PI / 2)
                            ctx.drawImage(this, 0, -imgHeight, imgWidth, imgHeight)
                            break
                        case 3:// 旋转180度
                            canvas.width = imgWidth
                            canvas.height = imgHeight
                            ctx.rotate(Math.PI)
                            ctx.drawImage(this, -imgWidth, -imgHeight, imgWidth, imgHeight)
                            break
                        case 8: // 旋转-90度
                            canvas.width = imgHeight
                            canvas.height = imgWidth
                            ctx.rotate(3 * Math.PI / 2)
                            ctx.drawImage(this, -imgWidth, 0, imgWidth, imgHeight)
                            break
                        default:
                            ctx.drawImage(this, 0, 0, imgWidth, imgHeight)
                    }
                    let dataUrl = canvas.toDataURL("image/jpeg")// canvase 转为base64
                    file = dataURLtoBlob(dataUrl) // base64转为blog
                    resolve(file)
                }
            } else {
                resolve(file)
            }

        })
    }))
}

function dataURLtoBlob(dataUrl) {
    let arr = dataUrl.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})
}

export default transformImg