swiper/core/update/updateProgress.js

export default function updateProgress(translate) {
  const swiper = this;

  if (typeof translate === 'undefined') {
    const multiplier = swiper.rtlTranslate ? -1 : 1; // eslint-disable-next-line

    translate = swiper && swiper.translate && swiper.translate * multiplier || 0;
  }

  const params = swiper.params;
  const translatesDiff = swiper.maxTranslate() - swiper.minTranslate();
  let {
    progress,
    isBeginning,
    isEnd
  } = swiper;
  const wasBeginning = isBeginning;
  const wasEnd = isEnd;

  if (translatesDiff === 0) {
    progress = 0;
    isBeginning = true;
    isEnd = true;
  } else {
    progress = (translate - swiper.minTranslate()) / translatesDiff;
    isBeginning = progress <= 0;
    isEnd = progress >= 1;
  }

  Object.assign(swiper, {
    progress,
    isBeginning,
    isEnd
  });
  if (params.watchSlidesProgress || params.centeredSlides && params.autoHeight) swiper.updateSlidesProgress(translate);

  if (isBeginning && !wasBeginning) {
    swiper.emit('reachBeginning toEdge');
  }

  if (isEnd && !wasEnd) {
    swiper.emit('reachEnd toEdge');
  }

  if (wasBeginning && !isBeginning || wasEnd && !isEnd) {
    swiper.emit('fromEdge');
  }

  swiper.emit('progress', progress);
}