h5上传大文件可能会导致手机浏览器卡死，重新刷新的问题

一般来说我们会使用crypto获取hash值，如果代码是这样的

javascript 复制代码

export const calculateHash = (file) => {
    return new Promise((resolve, reject) => {
        const reader = new FileReader();
        reader.onload = function () {
            const arrayBuffer = reader.result;
            // 使用CryptoJS计算SHA-256哈希
            const wordArray = CryptoJS.lib.WordArray.create(arrayBuffer);
            const hash = CryptoJS.SHA256(wordArray).toString(CryptoJS.enc.Hex);
            resolve(hash);
        };
        reader.onerror = reject;
        reader.readAsArrayBuffer(file);
    });
}

reader.readAsArrayBuffer(file);

会一次性读完整个文件，造成内存暴涨，所以需要修改hash值问题，两个方案

方案1：

❌ 前端不算 hash

✅ 后端生成 key（UUID）

✅ 前端直接上传

方案2：

前端只算前 5MB + 后 5MB

拼一个"弱 hash"

用于去重，不阻塞 UI

方案2代码：

javascript 复制代码

export const calculateWeakHash = (file, chunkSize = 5 * 1024 * 1024) => {
    return new Promise((resolve, reject) => {
        const size = file.size

        // 小文件直接走全量
        if (size <= chunkSize * 2) {
            return calculateFullHash(file).then(resolve).catch(reject)
        }

        const firstChunk = file.slice(0, chunkSize)
        const lastChunk = file.slice(size - chunkSize, size)

        const reader1 = new FileReader()
        const reader2 = new FileReader()

        let buffer1, buffer2

        reader1.onload = () => {
            buffer1 = reader1.result
            if (buffer2) finish()
        }

        reader2.onload = () => {
            buffer2 = reader2.result
            if (buffer1) finish()
        }

        reader1.onerror = reader2.onerror = reject

        reader1.readAsArrayBuffer(firstChunk)
        reader2.readAsArrayBuffer(lastChunk)

        function finish() {
            const hash = CryptoJS.SHA256(
                CryptoJS.lib.WordArray.create(
                    concatArrayBuffer(buffer1, buffer2, size)
                )
            ).toString(CryptoJS.enc.Hex)

            resolve(hash)
        }
    })
}

function concatArrayBuffer(buf1, buf2, fileSize) {
    const sizeBuffer = new Uint8Array(8)
    new DataView(sizeBuffer.buffer).setBigUint64(0, BigInt(fileSize))

    const tmp = new Uint8Array(
        sizeBuffer.byteLength + buf1.byteLength + buf2.byteLength
    )

    tmp.set(sizeBuffer, 0)
    tmp.set(new Uint8Array(buf1), sizeBuffer.byteLength)
    tmp.set(new Uint8Array(buf2), sizeBuffer.byteLength + buf1.byteLength)

    return tmp.buffer
}