The return statement ends function execution and specifies a value to be returned to the function caller. return ^MDN

There are a few missteps here aside from not returning a value. return is the facility to send a value back from a function, but in order for that to happen, no errors can occur. As it stands, the variable color is used in the switch statement, but it does not exist, perhaps because it was supposed to be fruit or vice versa. Further, the values in the resulting code for the case statements are basically just references to variables, and if there is no variable named green then it is just undefined. Perhaps you meant green.

function fruitColor(fruit) {

 //note that there was no value color here, there was only the accepted

 //parameter fruit, which should either be used or changed to color

 switch(color) {

  case apple : 

   //needs quotes, green with no quotes is a variable reference

   green;

   //note that simply using the string green doesn't accomplish anything though

   //what we really need to do is send a value back, and in JavaScript you

   //use the return keyword for that followed by the returning value

   return green;//like this

    break;

  case banana : yellow;//^

    break;

  case kiwi : green;//^

    break;

  case plum : red;//^

    break;

 }

}

var result = fruitColor(plum);//needs quotes, plum would be a variable refernce

Personally, I prefer dictionaries for this type of work.

var fruitColors = {

 apple : green,

 banana : yellow,

 kiwi : green,

 plum : red

};

var plumColor = fruitColors[plum];//red