javascript - 这里返回真假有什么用？

Question

function userid_validation(uid, mx, my) {
  var uid_len = uid.value.length;

  if (uid_len == 0 || uid_len >= my || uid_len < mx) {
    alert("User Id should not be empty / length be between " + mx + " to " + my);
    uid.focus(); //is this focus will be on alert box?  
    return false; //what is use of this false ?
  }

  return true; //what is use of this true?
}

Answer 1

我想它可以防止事件冒泡。防止链接和表单的标准行为（防止重定向和提交）是常见的做法。

Answer 2

如果没有看到代码是从哪里调用的，就不能完全确定......但很可能它是从 DOM0 事件处理程序（由 分配的<element>.onclick=）调用的

false 将阻止默认操作发生，而 true 将允许它发生。

function userid_validation(uid,mx,my)
{
  var uid_len = uid.value.length;
  if (uid_len == 0 || uid_len >= my || uid_len < mx)
  {
    alert("User Id should not be empty / length be between "+mx+" to "+my);
    uid.focus(); //is this focus will be on alert box?
    return false; //what is use of this false ? 
  }
return true; //what is use of this true? 
}