Improve Nested Conditionals（优化嵌套

//method1
     if (color) {
         if (color === 'black') {
             printBlackBackground();
         } else if (color === 'red') {
             printRedBackground();
         } else if (color === 'blue') {
             printBlueBackground();
         } else if (color === 'green') {
             printGreenBackground();
         } else {
             printYellowBackground();
         }
     }
     
 //method2
     switch(color) {
         case 'black':
             printBlackBackground();
             break;
         case 'red':
             printRedBackground();
             break;
         case 'blue':
             printBlueBackground();
             break;
         case 'green':
             printGreenBackground();
             break;
         default:
             printYellowBackground();
     }
     
 //method3
     switch(true) {
         case (typeof color === 'string' && color === 'black'):
             printBlackBackground();
             break;
         case (typeof color === 'string' && color === 'red'):
             printRedBackground();
             break;
         case (typeof color === 'string' && color === 'blue'):
             printBlueBackground();
             break;
         case (typeof color === 'string' && color === 'green'):
             printGreenBackground();
             break;
         case (typeof color === 'string' && color === 'yellow'):
             printYellowBackground();
             break;
     }
     
 //method4
     var colorObj = {
         'black': printBlackBackground,
         'red': printRedBackground,
         'blue': printBlueBackground,
         'green': printGreenBackground,
         'yellow': printYellowBackground
     };
     if (color in colorObj) {
       colorObj[color]();
     }