aliapp-demo/page/API/download-file/download-file.js

Page({
  download() {
    my.downloadFile({
      url: 'http://img.alicdn.com/tfs/TB1x669SXXXXXbdaFXXXXXXXXXX-520-280.jpg',
      success({ apFilePath }) {
        my.previewImage({
          urls: [apFilePath],
        });
      },
      fail(res) {
        my.alert({
          content: res.errorMessage || res.error,
        });
      },
    });
  },
})