<ul>
    <li v-for="img in list">
        <img v-lazy="img.src" />
    </li>
</ul>

this.renderLoading(() => {
    this.attempt++;
    this.options.adapter["beforeLoad"] &&
        this.options.adapter["beforeLoad"](this, this.options);
    this.record("loadStart");
    loadImageAsync(
        {
            src: this.src,
            cors: this.cors,
        },
        (data) => {
            this.naturalHeight = data.naturalHeight;
            this.naturalWidth = data.naturalWidth;
            this.state.loaded = true;
            this.state.error = false;
            this.record("loadEnd");
            this.render("loaded", false);
            this.state.rendered = true;
            this._imageCache.add(this.src);
            onFinish();
        },
        (err) => {
            !this.options.silent && console.error(err);
            this.state.error = true;
            this.state.loaded = false;
            this.render("error", false);
        }
    );
});

  /*
   * render loading first
   * @params cb:Function
   * @return
   */
  renderLoading (cb) {
    this.state.loading = true
    loadImageAsync({
      src: this.loading,
      cors: this.cors
    }, data => {
      this.render('loading', false)
      this.state.loading = false
      cb()
    }, () => {
      // handler `loading image` load failed
      cb()
      this.state.loading = false
      if (!this.options.silent) console.warn(`VueLazyload log: load failed with loading image(${this.loading})`)
    })
  }

const loadImageAsync = (item, resolve, reject) => {
    let image = new Image();
    if (!item || !item.src) {
        const err = new Error("image src is required");
        return reject(err);
    }
    image.src = item.src;
    if (item.cors) {
        image.crossOrigin = item.cors;
    }
    image.onload = function () {
        resolve({
            naturalHeight: image.naturalHeight,
            naturalWidth: image.naturalWidth,
            src: image.src,
        });
    };
    image.onerror = function (e) {
        reject(e);
    };
};

   /**
         * set element attribute with image'url and state
         * @param  {object} lazyload listener object
         * @param  {string} state will be rendered
         * @param  {bool} inCache  is rendered from cache
         * @return
         */
    _elRenderer (listener, state, cache) {
      if (!listener.el) return
      const { el, bindType } = listener
      let src
      switch (state) {
        case 'loading':
          src = listener.loading
          break
        case 'error':
          src = listener.error
          break
        default:
          src = listener.src
          break
      }
      if (bindType) {
        el.style[bindType] = 'url("' + src + '")'
      } else if (el.getAttribute('src') !== src) {
        el.setAttribute('src', src)
      }
      el.setAttribute('lazy', state)
      this.$emit(state, listener, cache)
      this.options.adapter[state] &&
                this.options.adapter[state](listener, this.options)
      if (this.options.dispatchEvent) {
        const event = new CustomEvent(state, {
          detail: listener
        })
        el.dispatchEvent(event)
      }
    }

if (this._imageCache.has(this.src)) {
    this.state.loaded = true;
    this.render("loaded", true);
    this.state.rendered = true;
    return onFinish();
}

function throttle(action, delay) {
    let timeout = null;
    let movement = null;
    let lastRun = 0;
    let needRun = false;
    return function () {
        needRun = true;
        if (timeout) {
            return;
        }
        let elapsed = Date.now() - lastRun;
        let context = this;
        let args = arguments;
        let runCallback = function () {
            lastRun = Date.now();
            timeout = false;
            action.apply(context, args);
        };
        if (elapsed >= delay) {
            runCallback();
        } else {
            timeout = setTimeout(runCallback, delay);
        }
        if (needRun) {
            clearTimeout(movement);
            movement = setTimeout(runCallback, 2 * delay);
        }
    };
}

function getBestSelectionFromSrcset(el, scale) {
    if (el.tagName !== "IMG" || !el.getAttribute("data-srcset")) return;
    let options = el.getAttribute("data-srcset");
    const result = [];
    const container = el.parentNode;
    const containerWidth = container.offsetWidth * scale;
    let spaceIndex;
    let tmpSrc;
    let tmpWidth;
    options = options.trim().split(",");
    options.map((item) => {
        item = item.trim();
        spaceIndex = item.lastIndexOf(" ");
        if (spaceIndex === -1) {
            tmpSrc = item;
            tmpWidth = 999998;
        } else {
            tmpSrc = item.substr(0, spaceIndex);
            tmpWidth = parseInt(
                item.substr(spaceIndex + 1, item.length - spaceIndex - 2),
                10
            );
        }
        result.push([tmpWidth, tmpSrc]);
    });
    result.sort(function (a, b) {
        if (a[0] < b[0]) {
            return 1;
        }
        if (a[0] > b[0]) {
            return -1;
        }
        if (a[0] === b[0]) {
            if (b[1].indexOf(".webp", b[1].length - 5) !== -1) {
                return 1;
            }
            if (a[1].indexOf(".webp", a[1].length - 5) !== -1) {
                return -1;
            }
        }
        return 0;
    });
    let bestSelectedSrc = "";
    let tmpOption;
    for (let i = 0; i < result.length; i++) {
        tmpOption = result[i];
        bestSelectedSrc = tmpOption[1];
        const next = result[i + 1];
        if (next && next[0] < containerWidth) {
            bestSelectedSrc = tmpOption[1];
            break;
        } else if (!next) {
            bestSelectedSrc = tmpOption[1];
            break;
        }
    }
    return bestSelectedSrc;
}

  /*
   *  check el is in view
   * @return {Boolean} el is in view
   */
  checkInView () {
    this.getRect()
    return (this.rect.top < window.innerHeight * this.options.preLoad && this.rect.bottom > this.options.preLoadTop) &&
            (this.rect.left < window.innerWidth * this.options.preLoad && this.rect.right > 0)
  }

   /**
    * init IntersectionObserver
    * set mode to observer
    * @return
    */
    _initIntersectionObserver () {
      if (!hasIntersectionObserver) return
      this._observer = new IntersectionObserver(this._observerHandler.bind(this), this.options.observerOptions)
      if (this.ListenerQueue.length) {
        this.ListenerQueue.forEach(listener => {
          this._observer.observe(listener.el)
        })
      }
    }