If you go to ideone.com, select javascript as the language, then click the sample link, you’ll see something like one of these depending upon which flavour of javascript you chose:
while((num = readline()) != 42) {
print(num);
}
or
importPackage(java.io);
importPackage(java.lang);
var reader = new BufferedReader( new InputStreamReader(System['in']) );
while(true) {
var line = reader.readLine();
if(line == null || line == "42") {
break;
} else {
System.out.println(line);
}
}