计算文件hash,使用到了模块 js-sha1

该模块文档：GitHub - emn178/js-sha1: A simple SHA1 hash function for JavaScript supports UTF-8 encoding.

 主要思路就是通过内置方法 slice 分块按顺序计算hash值

javascript">import sha1 from 'js-sha1'

export async function ContentHash(file, progress) {

    return new Promise((resolve, reject) => {
        const chunkSize = 50 * 1024 * 1024
        let promise = Promise.resolve()
        for (let index = 0; index < file.size; index += chunkSize) {
            promise = promise.then(() => hashBlob(file.slice(index, index + chunkSize)))
        }
        let count = 0
        const hash = sha1.create()

        function hashBlob(blob) {
            return new Promise((resolve, reject) => {
                const reader = new FileReader()
                reader.onload = ({target}) => {
                    hash.update(target.result)
                    count += 1
                    resolve()
                }
                reader.onerror = function (event) {
                    reject(event)
                }
                reader.onprogress = function (event) {
                    if (event) {
                        progress = Math.ceil((event.loaded + count * chunkSize) * 100 / progress.file_size)
                    }
                }
                reader.readAsArrayBuffer(blob)
            })
        }

        promise.then(async () => {
            const conHash = hash.hex().toUpperCase()
            resolve({conHash})
        }).catch(() => {
            reject()
        })
    })
}