bolb、bloburl、file、base64间的转换

bloburl格式：

　　blob:http://localhost:8080/c69fbb0e-b234-4926-bb3e-aa6103a169fa

blob格式：

　　Blob {size: 272260, type: 'application/pdf'}size: 272260type: "application/pdf"[[Prototype]]: Blob

file格式：

　　

base64格式：

　　data:application/pdf;base64,JVBERi0xLjMKJbrfrOAKMyAwIG9iag...

1.bloburl转换为file

　　　　httpRequest(src) {
            let that = this
            return new Promise((resolve, reject) => {
                let xhr = new XMLHttpRequest()
                xhr.open('GET', src, true)
                xhr.responseType = 'blob'
                xhr.onload = function (e) {
                    if (this.status == 200) {
                        let myBlob = this.response
                        let files = new window.File(
                            [myBlob],
                            that.objData.prj_no + '.pdf',
                            { type: myBlob.type }
                        ) // myBlob.type 自定义文件名
                        resolve(files)
                    } else {
                        reject(false)
                    }
                }
                xhr.send()
            })
        },

 

2.file转换为base64

        getBase64(file) {
            return new Promise((resolve, reject) => {
                const reader = new FileReader()
                reader.readAsDataURL(file)
                reader.onload = () => resolve(reader.result)
                reader.onerror = (error) => reject(error)
            })
        },    

3.base64转换为file

        base64ImgtoFile(dataurl, filename = 'file') {
            const arr = dataurl.split(',')
            const mime = arr[0].match(/:(.*?);/)[1]
            const suffix = mime.split('/')[1]
            const bstr = atob(arr[1])
            let n = bstr.length
            const u8arr = new Uint8Array(n)
            while (n--) {
                u8arr[n] = bstr.charCodeAt(n)
            }
            return new File([u8arr], `${filename}.${suffix}`, {
                type: mime,
            })
        },    

4.base64转换为blob

　　　　dataURLtoBlob(dataurl) {
            var 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 })
        },

　　

5.blob转换为base64

    blobToDataURL(blob, callback) {
            let a = new FileReader()
            a.onload = function (e) {
                callback(e.target.result)
            }
            a.readAsDataURL(blob)
    },