js实现下载（文件流、文件链接）

JS可以使用`XMLHttpRequest`对象来实现文件下载。以下是两种方式：

1. 下载文件流

function downloadFile(data, fileName) {
  let blob = new Blob([data]);
  if (window.navigator.msSaveOrOpenBlob) {
    // IE10+
    window.navigator.msSaveOrOpenBlob(blob, fileName);
  } else {
    let link = document.createElement("a");
    if (link.download !== undefined) {
      let url = URL.createObjectURL(blob);
      link.setAttribute("href", url);
      link.setAttribute("download", fileName);
      link.style.visibility = "hidden";
      document.body.appendChild(link);
      link.click();
      document.body.removeChild(link);
    }
  }
}

使用方式：

let data = '这是文件流的数据';
let fileName = 'file.txt';
downloadFile(data, fileName);

2. 下载文件链接

function downloadFile(url, fileName) {
  let link = document.createElement("a");
  link.setAttribute("href", url);
  link.setAttribute("download", fileName);
  link.style.visibility = "hidden";
  document.body.appendChild(link);
  link.click();
  document.body.removeChild(link);
}

使用方式：

let url = 'http://www.example.com/file.txt';
let fileName = 'file.txt';
downloadFile(url, fileName);