if-prompt.js

来自「这是《JavaScript学习源代码》一书的源代码」· JavaScript 代码 · 共 10 行

// initialize a variable with a null value
var username = null;

if ( username == null )
{
  // ask the user for their name
  username = prompt( "Please Enter Your Name", "" );
  // ... or greet the user by name
  if ( username != "" ) alert( "Welcome " + username );
}