Proof that downloads are blocked in modern Excel add-ins. Written while developing Excel2LaTeX.

Excel Add-in Download Blocked PoC.EXCEL.yaml

name: Excel Add-in Download Blocked PoC
description: Proof that downloads are blocked in modern Excel add-ins. Written while developing Excel2LaTeX.
host: EXCEL
api_set: {}
script:
  content: >
    document.getElementById("test").addEventListener("click", function(event) {
      console.log(File);
      var blob = new Blob(["foo"], {
        type: "text/plain"
      });

      let url = window.URL.createObjectURL(blob);
      url = url.slice(5);
      console.log(url);
      var a = document.getElementById("test2");
      a.href = url;

      run();
    });


    document.getElementById("test2").addEventListener("click", function (event)
    {
      let url = document.getElementById("test2").href;
      console.log(url);
      URL.revokeObjectURL(url);
    });


    function run() {
      Excel.run(async (context) => {
        const range = context.workbook.getSelectedRange();
        range.load(["values"]);
        const cellProps = range.getCellProperties({
          address: true,
          format: {
            fill: {
              color: true
            },
            font: {
              color: true
            }
          },
          style: true
        });
        await context.sync();

        return toLatex(range.values.map((row, i) => row.map((value, j) => [value, cellProps.value[i][j].format])));
      }).then((text) => {
        console.log(text);
        const node = document.getElementById("container");
        node.innerText = text;
        const selection = window.getSelection();
        const range = document.createRange();
        range.selectNodeContents(node);
        selection.removeAllRanges();
        selection.addRange(range);
        document.execCommand("copy");
      });
    }


    /** Default helper for invoking an action and handling errors. */

    async function tryCatch(callback) {
      try {
        await callback();
      } catch (error) {
        // Note: In a production add-in, you'd want to notify the user through your add-in's UI.
        console.error(error);
      }
    }


    function toLatex(range) {
      console.log(range);
      let packages = {
        color: "",
        strikethrough: "",
        subscript: ""
      };
      let body = "\\begin{tabular}";
      for (let row of range) {
        for (let cell of row) {
          cell[0] = cell[0].toString(); // cells can be strings, numbers or bools
          if (cell[0] === "") cell[0] = " ";
          let [p, text] = applyFormat(packages, cell);
          packages = p;
          body += `${text}`;
        }
        row = row.join(" & ") + "\\\\";
      }
      return Object.values(packages).join("") + body + "\\end{tabular}";
    }


    // Only applies if format applied to entire cell, not just letters

    function applyFormat(packages, [value, format]) {
      if (format.font.bold) value = `\\textbf{${value}}`;
      if (format.font.color !== "#000000") {
        if (!packages.color) packages.color = "\\usepackage{xcolor}\n";
        value = `\\textcolor{${format.font.color}}{${value}}`;
      }
      if (format.font.italic) value = `\\textit{${value}}`;
      // apply font?
      // don't change font size
      if (format.font.strikethrough) {
        if (!packages.strikethrough) packages.strikethrough = "\\usepackage{cancel}\n";
        value = `\\cancel{${value}}`;
      }
      if (format.font.subscript) {
        if (!packages.subscript) packages.subscript = "\\usepackage{fixltx2e}\n";
        value = `\\textsubscript{${value}}`;
      }
      if (format.font.superscript) value = `\\textsuperscript{${value}}`;
      if (format.font.underline) value = `\\underline{${value}}`;
      return [packages, value];
    }
  language: typescript
template:
  content: "<section class=\"ms-font-m\">\n\t<p class=\"ms-font-m\">This sample demonstrates basic Excel API calls.</p>\n</section>\n\n<section class=\"samples ms-font-m\">\n\t<h3>Try it out</h3>\n\t<p class=\"ms-font-m\">Select some cells in the worksheet, then press <b>Highlight selected range</b>.</p>\n\t<button id=\"run\" class=\"ms-Button\">\n        <span class=\"ms-Button-label\">Highlight selected range</span>\n    </button>\n</section>\n\n<button id=\"test\">\n\tboop\n</button>\n\n<a id=\"test2\" href=\"https://www.google.com/robots.txt\" download>\n\tbeep\n</a>\n\n<p id=\"container\"></p>"
  language: html
style:
  content: |-
    section.samples {
        margin-top: 20px;
    }

    section.samples .ms-Button, section.setup .ms-Button {
        display: block;
        margin-bottom: 5px;
        margin-left: 20px;
        min-width: 80px;
    }
  language: css
libraries: |-
  https://appsforoffice.microsoft.com/lib/1/hosted/office.js
  @types/office-js

  office-ui-fabric-js@1.4.0/dist/css/fabric.min.css
  office-ui-fabric-js@1.4.0/dist/css/fabric.components.min.css

  core-js@2.4.1/client/core.min.js
  @types/core-js

  jquery@3.1.1
  @types/jquery@3.3.1

  file-saver@2.0.2
  @types/file-saver@2.0.2

  @types/node