Covert some code from javascript to Groovy script

Working code in Groovy

def handler = [(~/^Mac OS.*/) : { "open $it".execute() }, (~/^Windows.*/) : { "cmd /C start $it".execute() },
(~/.*/) : {
//--- Open chrome in desktop machine
def browsers =[ 'firefox'.'chrome' ]
//--- find a browser we know the location of
def browser = browsers.find {
"which $it".execute().waitFor() == 0
}
//--- and run it if one found
if( browser )
"$browser $it".execute()
}
]
def k = handler.find { k, v -> k.matcher( System.properties.'os.name' ).matches() }
k?.value( delegate )
}
"URL".browse()

Need to convert javascript to in groovy script

document.getElementById("username-field").value = "UserName";
document.getElementById("password-field").value = "Password";
document.getElementById("login_submit").click();

console.log(localStorage.getItem("access_token"));