文件下载重命名时扩展名被误判怎么办？

export const downloadFile = (fileUrl, fileName, errorCallback) => {
    try {
        const xhr = new XMLHttpRequest();
        xhr.open("get", fileUrl, true);
        xhr.responseType = "blob";
        xhr.onload = function () {
            if (this.status === 200 || this.status === 304) {
                const contentType = this.getResponseHeader("Content-Type");
                let ext = "";
                if (contentType) {
                    const contentTypeParts = contentType.split('/');
                    if (contentTypeParts.length === 2) {
                        ext = `.${contentTypeParts[1]}`;
                    }
                }
                const blob = new Blob([this.response], { type: contentType });
                const url = URL.createObjectURL(blob);
                const finalFileName = fileName + ext; 
                simulateClick(blob, finalFileName, "_blank");
                URL.revokeObjectURL(url);
            }
        };
        xhr.onerror = function () {
            errorCallback && errorCallback();
        };
        xhr.send();
    } catch (error) {
        errorCallback && errorCallback();
    }
};