js implements form validation function

<form action="demo.html" onsubmit="return checkForm()">
      <div>
      <div class="text">
           <p>Username</p>
           <input id="value" onfocus="shoeTips('hint','Username length cannot be less than six')" onblur="hint_hide()" onkeyup="hint()" type="text" Name="Userame" placeholder="Username" />
           <span id="hint"></span>
          </div>
         <div class="text">
           <p>Password</p>
           <input id="pass_value" onfocus="shoeTips('pass_hint','The password length cannot be less than six')" onblur="pass_hide()" onkeyup="checkPass()" type="password" name="password" placeholder="password" />
            <span id="pass_hint"></span>
            </div>
            <div class="text">
              <p>Confirm Password</p>
              <input id="passpass_value" onfocus="shoeTips('passpass_hint','The two passwords must be consistent')" onblur="passpass_hide()" onkeyup="checkPassPass()" type="password" name="password" placeholder="Confirm password" />
              <span id="passpass_hint"></span>
           </div>
           <div class="text">
                    <p>Email</p>
                    <input id="email" onfocus="shoeTips('email_hint','The email format must be correct')" onblur="emailHide()" onkeyup="emailCheck()" type="email" name="email" placeholder="Email" />
                    <span id="email_hint"></span>
                </div>
                <div class="text">
                    <p>Mobile phone number</p>
                    <input id="phone" type="text" onfocus="shoeTips('phone_hint','A phone number in the format of eleven digits')" onblur="phoneHide()" onkeyup="phoneCheck()" Name="Phone" placeholder="Phone number">
                    <span id="phone_hint"></span>
                </div>
                <div class="submit">
             <input type="submit" value="Submit" />
         </div>
    </div>
</form>

function shoeTips(spanId, tips) {
 var span = document.getElementById(spanId);
 span.innerHTML = tips;
}
/**
 * Verify username */
function hint() {
 var value = document.getElementById("value").value;
 var hint = document.getElementById("hint");
 if(value.length < 6) {
  hint.innerHTML = "Username is too short";
  return false;
 } else {
  hint.innerHTML = "Qualified Username";
  return true;
 }
}
 
function hint_hide() {
 var hint = document.getElementById("hint");
 hint.innerHTML = "";
}
/**
 * Verify password */
 
function checkPass() {
 var value = document.getElementById("pass_value").value;
 var hint = document.getElementById("pass_hint");
 if(value.length < 6) {
  hint.innerHTML = "The password is too short";
  return false;
 } else {
  hint.innerHTML = "Password format is qualified";
  return true;
 }
}
 
function pass_hide() {
 var hint = document.getElementById("pass_hint");
 hint.innerHTML = "";
}
/***
 * Confirm password verification */
function checkPassPass() {
 var papavalue = document.getElementById("passpass_value").value;
 var value = document.getElementById("pass_value").value;
 var papahint = document.getElementById("passpass_hint");
 if(papavalue != value) {
  papahint.innerHTML = "The two passwords do not match";
  return false;
 } else {
  papahint.innerHTML = "";
  return true;
 }
}
 
function passpass_hide() {
 var papahint = document.getElementById("passpass_hint");
 papahint.innerHTML = "";
}
/**
 * Verify email address */
function checkEmail(strEmail) 
{      
    var emailReg = /^([a-zA-Z0-9_-])+@([a-zA-Z0-9_-])+(\.[a-zA-Z0-9_-])+/;
    if ( emailReg.test(strEmail) ) {
        return true;
    }
    else {
// alert("The email address you entered is not in the correct format!");
        return false;
    }
};
function emailCheck() {
 var emailValue = document.getElementById("email").value;
 var email_hint = document.getElementById("email_hint");
 var flag = checkEmail(emailValue);
 if(flag) {
  email_hint.innerHTML = "The email format is correct";
  return true;
 } else {
  email_hint.innerHTML = "Email format error";
  return false;
 }
}
 
function emailHide() {
 var email_hint = document.getElementById("email_hint");
 email_hint.innerHTML = "";
}
/**
 * Verify mobile phone number */
function checkMobile( strMobile )
{ //13588888888
    var regu = /^[1][345678][0-9]{9}$/;
    var re = new RegExp(regu);
    if (re.test(strMobile)) {
        return true;
    }
    else {
        return false;
    }
};
function phoneCheck() {
 var phone = document.getElementById("phone").value;
 var phone_hint = document.getElementById("phone_hint");
 var flag = checkMobile(phone);
 if(flag) {
  phone_hint.innerHTML = "The phone number format is correct";
  return true;
 } else {
  phone_hint.innerHTML = "The phone number format is incorrect";
  return false;
 }
}
 
function phoneHide() {
 var phone_hint = document.getElementById("phone_hint");
 phone_hint.innerHTML = "";
}
 
function checkForm() {
 var flag = emailCheck() && checkPass() && checkPassPass() && hint() && phoneCheck();
 return flag;
}