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ResizeObserver polyfill

For ancient browsers

此脚本不应直接安装。它是供其他脚本使用的外部库，要使用该库请加入元指令 // @require https://update.cn-greasyfork.org/scripts/435127/986124/ResizeObserver%20polyfill.js 

class ResizeObserver {
  constructor(callback) {
    this.observables = [];
      // Array of observed elements that looks like this:
      // [{
      //   el: domNode,
      //   size: {height: x, width: y}
      // }]
    this.boundCheck = this.check.bind(this);
    this.boundCheck();
    this.callback = callback;
  }
  
  observe(el) {
    if (this.observables.some((observable) => observable.el === el)) {
      return;
    }
    const newObservable = {
      el: el,
      size: {
        height: el.clientHeight,
        width: el.clientWidth
      }
    }
    this.observables.push(newObservable);
  }
  
  unobserve(el) {
    this.observables = this.observables.filter((obj) => obj.el !== el);
  }
  
  disconnect() {
    this.observables = [];
  }
  
  check() {
    const changedEntries = this.observables.filter((obj) => {
      const currentHeight = obj.el.clientHeight;
      const currentWidth = obj.el.clientWidth;
      if (obj.size.height !== currentHeight || obj.size.width !== currentWidth) {
        obj.size.height = currentHeight;
        obj.size.width = currentWidth;
        return true;
      }
    }).map((obj) => obj.el);
    if (changedEntries.length > 0) {
      this.callback(changedEntries);
    }
    window.requestAnimationFrame(this.boundCheck);
  }
}