jQuery+CSS3+HTML5百叶窗下拉

代码片段：

 let memo = {};
  
  let memoize = function(width, scale, lean) {
        
    const memoKey = `${width}-${scale}-${lean}`;
    
    if (!memo[memoKey]) {
      
      const currentH = width * scale;
      
      const result = {
        leftSize:   Math.sqrt(currentH ** 2 + (width * (0.5 - lean)) ** 2),
        rightSize:  Math.sqrt(currentH ** 2 + (width * (0.5 + lean)) ** 2),
        leftAngle:  Math.atan(currentH / ((0.5 - lean) * width)),
        rightAngle: Math.atan(currentH / ((0.5 + lean) * width))
      };
      
      memo[memoKey] = result;      
      
      memoize.count++;
    }     
    return memo[memoKey];
  }