javascript - Both call and apply produce the same result for String.prototype.toUppercase when passing an array

I usually see that we should use an array in apply method and array of arguments in call method:

If I do the following (call method would return undefined):

var namelist = {
   f:'first name',
   l:'last name'
}
function func(a,b){
   console.log(this[a]+' '+this[b])
}


func.call(namelist,['f','l'])
//undefined undefined

func.apply(namelist,['f','l'])
//first name last name

But, look here both call and apply method works:

String.prototype.toUpperCase.call(['a','b','c']) //returns 'A,B,C'
String.prototype.toUpperCase.apply(['a','b','c']) //returns 'A,B,C'

Why the call method is working?

If I do use like this:

String.prototype.toUpperCase.call('a','b','c')
//this would return 'A' only.