overleaf/services/web/frontend/js/pages/marketing/homepage.js

import '../../marketing'

function homepageAnimation(homepageAnimationEl) {
  function createFrames(word, { buildTime, holdTime, breakTime }) {
    const frames = []
    let current = ''

    // Build up the word
    for (const char of word) {
      current += char
      frames.push({ before: current, time: buildTime })
    }

    // Hold the complete word
    frames.push({ before: current, time: holdTime })

    // Break down the word
    for (let i = word.length - 1; i > 0; i--) {
      current = word.substring(0, i)
      frames.push({ before: current, time: breakTime })
    }

    // Add the final frame with an empty string
    frames.push({ before: '', time: breakTime })

    return frames
  }

  const opts = {
    buildTime: 100,
    holdTime: 1000,
    breakTime: 100,
  }

  const frames = [
    // 1.5s pause before starting
    { before: '', time: 1500 },
    ...createFrames('articles', opts),
    ...createFrames('theses', opts),
    ...createFrames('reports', opts),
    ...createFrames('presentations', opts),
    // 5s pause on 'anything' frame
    ...createFrames('anything', { ...opts, holdTime: 5000 }),
  ]

  let index = 0
  function nextFrame() {
    const frame = frames[index]
    index = (index + 1) % frames.length

    homepageAnimationEl.innerHTML = frame.before
    setTimeout(nextFrame, frame.time)
  }

  nextFrame()
}

const homepageAnimationEl = document.querySelector('#home-animation-text')
const reducedMotionReduce = window.matchMedia(
  '(prefers-reduced-motion: reduce)'
)

if (homepageAnimationEl) {
  if (reducedMotionReduce.matches) {
    homepageAnimationEl.innerHTML = 'anything'
  } else {
    homepageAnimation(homepageAnimationEl)
  }
}