How to get return value from switch statement?

That's because when you're putting that into the Chrome console, you're short-circuiting it. It's just printing 'OK' because it's reaching the default case, not actually returning something.

If you want something returned, stick it in a function, and return the 'OK' from in the default case.

function switchResult(a){
    switch(a){
        default: 
            return "OK";
    }
}

var a = switchResult(3);

ES6 lets you do this using an immediately-invoked lambda:

const a = (() => {
  switch(3) {
    default: return "OK";
  }
})();

Perhaps interesting to note that you dont need the clutter of ;break; statements if you wrap it in a function. (as described by heloandre)

function switchResult(a){   
    switch(a){   
        case 1: return "FOO";
        case 2: return "BAR";
        case 3: return "FOOBAR";
        default: return "OK";      
    }
}
var a = switchResult(3);

No, the switch doesn't have a return value. What you see in the console is the return value of the statement inside the switch containing only a string literal value.

A statement can have a return value. An assignment for example has the assigned value as return value, and post-incrementing a value returns the result after incrementing:

> a = 42;
42
> a++;
43

A statement containing just a value will have that value as return value:

> 42;
42
> "OK";
"OK"

A statement like that is however only useful in the console, for example for showing the value of a variable. In code it won't accomplish anything.