How to check if String argument is equal to dictionary key

In my website I have a terminal where the user can enter "man lochlann" to return a description on what the command 'lochlann' does.

This input is of Type String. I would like to check if this String is a valid key in the dictionary 'MAN'.

var MAN_PRIVATE = {
  lochlann: "LOCHLANN<BR>lochlann - Returns a description for the best Software Developer to have ever lived<br>argument - NOT REQUIRED",
  mtu: "MTU<BR>mtu - Returns a description on Munster Technological University<br>argument - NOT REQUIRED",
}
var MAN_PUBLIC = {
  help: "HELP<br>help - provides the user with information on how to use the terminal<br>argument - NOT REQUIRED",
  bin: "BIN<br>bin - returns a list of all acceptable commands.<br>argument - NOT REQUIRED",
}
MAN = Object.assign({}, MAN_PRIVATE, MAN_PUBLIC);

command = "help";

executeMan(command);

function executeMan(command) {
    if (command in MAN) {         //this condition returns true
        console.log(MAN.help);    //this works
        console.log(MAN.command); //this does not work - returns 'undefined'
    }
}