A userscript that adds a card showing undone work to the Google Classroom Classes page.

ClassroomWorkCard.user.js

// ==UserScript==
// @name         Classroom Work Card
// @version      0.1.8
// @description  Adds a card showing undone work to the Google Classroom Classes page.
// @author       jrr6
// @downloadURL  https://gist.github.com/jrr6/5f7961a3e3a1b582fae94a92ee712250/raw/ClassroomWorkCard.user.js
// @updateURL    https://gist.github.com/jrr6/5f7961a3e3a1b582fae94a92ee712250/raw/ClassroomWorkCard.user.js
// @match        https://classroom.google.com/*
// @grant        GM_addStyle
// ==/UserScript==

function addCard () {
  var css = document.createElement('style')
  css.type = 'text/css'
  var styles = `
  #work-spot {
    width: 27.5rem;
    height: 20.5em;
    overflow: scroll;
    margin-bottom: 2rem;
    text-align: center;
    margin-right: 2.5rem;
    box-shadow: 0 0.1rem 0.2rem rgba(0,0,0,0.12), 0 0 0.1rem rgba(0,0,0,0.12);
    padding: 1em;
    background: #fff;
  }
  #work-spot:hover {
    box-shadow: 0 8px 10px 1px rgba(0,0,0,0.14), 0 3px 14px 2px rgba(0,0,0,0.12), 0 5px 5px -3px rgba(0,0,0,0.2);
  }
  #work-spot h1 {
    font-size: 2rem;
    font-weight: 500;
    line-height: 2.8rem;
  }
  .work-item h3 {
      font-weight: bold;
  }
  #work-spot h2 {
      color: gray;
      font-weight: bold;
  }
  .work-item {
      border: 1px solid black;
      margin-bottom: 1em;
      padding: 0.5em;
  }
  `
  if (css.styleSheet) {
    css.styleSheet.cssText = styles
  } else {
    css.appendChild(document.createTextNode(styles))
  }
  document.getElementsByTagName('head')[0].appendChild(css)

  var workSpot = document.createElement('div')
  workSpot.setAttribute('id', 'work-spot')
  var h1 = document.createElement('h1')
  h1.textContent = 'Undone Work'
  workSpot.appendChild(h1)
  document.querySelector('.JwPp0e').prepend(workSpot)

  // script
  var dates = ['Sunday', 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday']
  var todayIdx = (new Date()).getDay()
  dates = dates.splice(todayIdx).concat(dates)
  var asgns = []
  document.querySelectorAll('div.kdAl3b div[jscontroller="x4VfFc"]').forEach(e => {
    let assignmentGroups = Array.from(e.children).filter(e => e.classList.contains('hrUpcomingAssignmentGroup'))
    assignmentGroups.forEach(e => {

      let dueDate = e.previousSibling.textContent.slice(4)
      let className = e.parentElement.parentElement.parentElement.children[0].children[2].children[0].children[0].children[0].children[0].textContent
      for (let child of e.children) {
        let asgnName = child
        asgns.push({date: dueDate, classN: className, nameNode: asgnName})
      }
    })
  })
  asgns.sort((a, b) => {
    let aIdx = dates.indexOf(a.date)
    let bIdx = dates.indexOf(b.date)
    // special cases
    if (a.date === 'today' && b.date === 'today') {
        return 0
    } else if (a.date === 'today') {
        return -1
    } else if (b.date === 'today') {
        return 1
    }
    if (a.date === 'tomorrow' && b.date === 'tomorrow') {
        return 0
    } else if (a.date === 'tomorrow') {
        return -1
    } else if (b.date === 'tomorrow') {
        return 1
    }
    if (aIdx === -1 && bIdx === -1) {
        return 0
    } else if (aIdx === -1) {
        return 1
    } else if (bIdx === -1) {
        return -1
    }
    return aIdx > bIdx ? 1 : aIdx === bIdx ? 0 : -1
  })

  var wList = document.getElementById('work-spot')
  if (asgns.length === 0) {
    wList.textContent = 'No more work!'
  } else {
    for (let i = 0; i < asgns.length; ++i) {
      let box = document.createElement('div')
      box.classList.add('work-item')
      
      if (i > 0) {
        if (asgns[i - 1].date !== asgns[i].date) {
          let date = document.createElement('h2')
          date.textContent = `Due ${asgns[i].date}`
          wList.appendChild(date)
        }
      } else {
        let date = document.createElement('h2')
        date.textContent = `Due ${asgns[i].date}`
        wList.appendChild(date)
      }

      let classN = document.createElement('h3')
      classN.textContent = asgns[i].classN
      box.appendChild(classN)

      box.appendChild(asgns[i].nameNode.cloneNode(true))
      wList.appendChild(box)
    }
  }
}

function rafAsync () {
  return new Promise(resolve => {
    requestAnimationFrame(resolve)
  })
}

function checkElements (selector) {
  if (document.querySelector(selector) === null) {
    return rafAsync().then(() => checkElements(selector))
  } else {
    return Promise.resolve(true)
  }
}

var mo = new MutationObserver(function () {
  if (document.querySelector('.JwPp0e') !== null) {
    checkElements('.gHz6xd.yckQJf.lziZub.k6fwTc').then(setTimeout(addCard, 3000))
    mo.disconnect()
  }
})
mo.observe(document.body, {attributes: false, childList: true, subtree: true})