React js downloading file url

Question

there

I am pretty new to web programing and currently working on a project which needs to download the file from server. And I have the following code but it is not working well. The http request it sent is not the one I expected... Details commented in the code. Thanks

onDownload() {
    const Files = this.props.files;
    const file = Files.findOne({ name: this.props.selectedFile.name });
    const filePath = file.fileSpec; //file path is like /test.txt

    var tempLink = document.createElement('a');


    // would like to send some http request like:"/user/test.txt"
    //to the server. But it sent some strange string...
    // I feel like I need to convert the format here but not sure how
    tempLink.href = '/user' + filePath; 

    tempLink.setAttribute('download', file);
    tempLink.setAttribute('target', '_blank');
    document.body.appendChild(tempLink);
    tempLink.click();
    document.body.removeChild(tempLink);
}