.toUpperCase() is not a function

Question

When name is all uppercase, then the function should shout back to the user. For example, when name is "JERRY" then the function should return the string "HELLO, JERRY!" The console logs error: .toUpperCase() is not a function.

var hello = "Hello, ";

function greet(name) {

  if (name == null) {
    console.log(hello + "my friend")
  } else if (name == name.toUpperCase()) {
    console.log(hello.toUpperCase() + name.toUpperCase())
  } else {
    console.log(hello + name);
  }
}

var names = ["jack", "john"]
greet(names);

Answer 1

names is an array. An array has no such function.

You probably want to call the greet function on every element of the array:

names.forEach(greet);

If you want the greet function to accept an array as argument then you could do

function greet(name) {
      if (Array.isArray(name)) {
            name.forEach(greet);
            return;
      }
      ...

but this kind of polymorphism is usually seen as a bad practice.

Answer 2

You could apply .toString() first, and then use .toUpperCase():

if (name == name.toString().toUpperCase())