Can I call JS function and how?

Question

Okey community,

function validate() {
  var name = document.getElementById("name").value;
  var p = document.getElementById("pname");
  
  console.log("validating");  // added by PM-77-1

  if (name === null) {
    p.className += " show";
    return false;
  } else {
    return true;
  }
}

.split {
  height: 100%;
  position: fixed;
  top: 0;
}

.left {
  left: 0;
  width: 40%;
}

.right {
  right: 0;
  width: 60%;
}

.form {
  margin: 30% 5% 30% 5%;
}

.input {
  margin: 2% 2% 2% 2%;
  height: 40px;
  width: 35%;
}

.lower {
  width: 76%;
}

h6 {
  background-color: #3399ff;
  margin-top: 0px;
  min-height: 50px;
  max-height: 50px;
  font-size: 32px;
  color: white;
}

button {
  background-color: #3399ff;
  color: white;
  width: 77%;
  min-height: 50px;
  border: none;
  border-radius: 5px;
  margin-top: 10%;
}

body {
  font-family: Futura Md BT;
}

#map_canvas {
  height: 100%;
}

.name {
  display: none;
}

.lastname {
  display: none;
}

.address {
  display: none;
}

.city {
  display: none;
}

.country {
  display: none;
}

.show {
  display: block;
  margin-top: 0px;
  margin-bottom: 0px;
  color: red;
}

<div class="split left">
  <center>
    <h6>User Details</h6>
    <div class="form">
      <form action="input.php" method="POST" onsubmit="event.preventDefault(); validate()">
        <p class="name" id="pname">Please enter First Name</p>
        <p class="lastname" id="lastname">Please enter Last Name</p>
        <p class="address" id="address">Please enter Street / Number</p>
        <p class="city" id="city">Please enter City</p>
        <p class="country" id="country">Please enter country</p>
        <input type="text" class="input" id="name" name="firstname" placeholder="First Name">
        <input type="text" class="input" id="lastname" name="lastname" placeholder="Last Name"><br>
        <input type="text" class="input lower" id="address" name="streetnumber" placeholder="Street / Number"><br>
        <input type="text" class="input lower" id="city" name="city" placeholder="City"><br>
        <input type="text" class="input lower" id="country" name="country" placeholder="Country"><br>
        <button type="submit" onclick="return validate()">Add User</button>
      </form>
    </div>
  </center>
</div>

Please test this and tell me why is it not working. I tried everything, but somehow my js is not triggering. I changed ids and everything. Plus tell me if I did right thing in the form with validating default because I am doing that for the first time. Thank you everyone, so much.

I use body onload (to start a google map) but I did not paste that part, it works fine.

Please help me with an example, Thank you so much community !!!

Answer 1

Your function validate is calling just fine, but some statements inside it are not executing quite well. A few issues here:

1- To add a class to the element p, use p.classList.add("className")

2- When users leave the name field blank, the value is an empty string (''), not null. So, instead of checking:

if (name === null)

Check instead for:

if(name == '')

//or, even shorter:
if(!name)

Therefore, the JS becomes:

function validate() {
  var name = document.getElementById("name").value;
  var p = document.getElementById("pname");

  console.log("validating");

  if (!name) {
    p.classList.add( "show");
    return false;
  } else {
    return true;
  }
}