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HTML

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!
Insecure Resource

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CSS

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JavaScript

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Babel includes JSX processing.

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HTML 

              
                <table>
  <tr>
    <th>Item</th>
    <th>Team</th>
    <th>Hours</th>
  </tr>
  <tr>
    <td>Designing the shop front</td>
    <td>Tigers</td>
    <td>200</td>
  </tr>
  <tr>
    <td>Developing the MVP</td>
    <td>Panthers</td>
    <td>500<br></td>
  </tr>
  <tr>
    <td>Feature request #999</td>
    <td>Panthers</td>
    <td>450</td>
  </tr>
  <tr>
    <td>Creating  sales pitches</td>
    <td>Lions</td>
    <td>1100<br></td>
  </tr>
  <tr>
    <td>Designing the Christmas banner</td>
    <td>Tigers<br></td>
    <td>130</td>
  </tr>
</table>
<br>

<a title="Bookmarklet calculating the grouped costs" href="javascript:(function()%7Balert(JSON.stringify(Array.from(document.querySelectorAll(%22tr%3Anth-of-type(n%2B2)%22)).reduce((acc%2C%20row)%20%3D%3E%20%7Bconst%20team%20%3D%20row.children%5B1%5D.textContent%3Bconst%20hours%20%3D%20%2Brow.children%5B2%5D.textContent%3Breturn%20%7B%20...acc%2C%20%5Bteam%5D%3A%20(acc%5Bteam%5D%20%7C%7C%200)%20%2B%20hours%20%7D%3B%7D%2C%7B%7D)))%7D)()">Calculate the grouped costs by clicking this bookmarklet!</a> (demo 1)

<br><br>

You can also try the <a href="javascript:(function()%7Blet%20groupedHourCounts%20%3D%20Array.from(document.querySelectorAll(%22tr%3Anth-of-type(n%2B2)%22)).reduce((acc%2C%20row)%20%3D%3E%20%7Bconst%20team%20%3D%20row.children%5B1%5D.textContent%3Bconst%20hours%20%3D%20%2Brow.children%5B2%5D.textContent%3Breturn%20%7B%20...acc%2C%20%5Bteam%5D%3A%20(acc%5Bteam%5D%20%7C%7C%200)%20%2B%20hours%20%7D%3B%7D%2C%20%7B%7D)%3Blet%20listItems%20%3D%20Object.keys(groupedHourCounts).map(key%20%3D%3E%20%60%3Cli%3E%24%7Bkey%7D%3A%20%24%7BgroupedHourCounts%5Bkey%5D%7D%3C%2Fli%3E%60).join(%22%5Cn%22)%3Blet%20doc%20%3D%20%60%3Chtml%3E%3Chead%3E%3Ctitle%3EGrouped%20counts%3C%2Ftitle%3E%3C%2Fhead%3E%3Cbody%3E%3Ch1%3EGrouped%20cost%20counts%3C%2Fh1%3E%3Cul%3E%24%7BlistItems%7D%3C%2Ful%3E%3Cinput%20type%3D%22button%22%20onclick%3D%22window.history.back()%3B%22%20value%3D%22Back%20to%20the%20example%22%3E%3C%2Fbody%3E%3C%2Fhtml%3E%60%3Bconsole.log(doc)%3Breturn%20doc%7D)()">bookmarklet document</a> (demo 2)

<p>
I used <a href="https://mrcoles.com/bookmarklet/">this bookmarklet encoder</a> to encode the JavaScript into a URI string that is allowed in the HTML attribute <code>href</code>. Doing this manually becomes a hassle!
</p>
!

CSS
!

JS 

              
                // all JavaScript here was converted to a URI and put into a link
// Use for example this encoder https://mrcoles.com/bookmarklet/

// DEMO 1 code
// extract the information from the table, group it in an object, and alert() the result

alert(
  JSON.stringify(
    Array.from(document.querySelectorAll("tr:nth-of-type(n+2)")).reduce(
      (acc, row) => {
        const team = row.children[1].textContent;
        const hours = +row.children[2].textContent;
        return { ...acc, [team]: (acc[team] || 0) + hours };
      },
      {}
    )
  )
);

// DEMO 2 code: present using a bookmarklet document
//
// This extracts the information from the table, groups it, and returns it as a HTML document in a string.
// The return value will be shown in a special javacript: link HTML document by the browser when clicked.
let groupedHourCounts = Array.from(
  document.querySelectorAll("tr:nth-of-type(n+2)")
).reduce((acc, row) => {
  const team = row.children[1].textContent;
  const hours = +row.children[2].textContent;
  return { ...acc, [team]: (acc[team] || 0) + hours };
}, {});

let listItems = Object.keys(groupedHourCounts)
  .map(key => `<li>${key}: ${groupedHourCounts[key]}</li>`)
  .join("\n");
let doc = `
<html>
  <head>
    <title>Grouped counts</title>
  </head>
  <body>
    <h1>Grouped cost counts</h1>
    <ul>
      ${listItems}
    </ul>
    <input type="button" onclick="window.history.back();" value="Back to the example">
  </body>
</html>
`;
console.log(doc);
return doc;

// NOTE: adding target="_blank" to your link makes the js execute in the wrong context somehow. You can't use it.

// Presentation option 3: you could also inject the answer back into the DOM.
// Take this as an exercise :)
!
999px

Console