What is the best way to display an error message for an invalid input using JavaScript?

Question

What is the best way to display an error message for an invalid input using JavaScript?

I am struggling to implement error messages for my form inputs using JavaScript. My attempts so far have not been successful and I need guidance on the correct approach.

I want to show an error message and prevent the form from being submitted if any errors are present.

<form novalidate>
      <label for="password">
         <input type="password" name="password" id="password" placeholder="Password*" required minlength="8" />
         <span id='pwmessage'></span>
      </label>
      <label for="confirmpassword">
        <input type="password" name="confirm_password" id="confirm_password" placeholder=" Confirm password*" required minlength="8" />
        <span id='cpwmessage'></span>
      </label>
      <button>Submit</button>
  </form>

javascript html css

Answer 1

Answer №1

Give this method a shot! In this scenario, the submission will not go through if either the password or confirm password fields are left empty, or if the confirm password does not match the initial password.

function checkEmpty() {
    if (document.getElementById("password").value == "") {
        document.getElementById("pwmessage").innerHTML = "Please enter at least one character in the password field";
        return false;
    }
    if (document.getElementById("confirm_password").value != document.getElementById("password").value) {
        document.getElementById("cpwmessage").innerHTML = "Kindly verify your password and try again";
        return false;
    };
}

<form novalidate action='process.php' method='get'>
    <label for="password">
       <input type="password" name="password" id="password" placeholder="Password*" required minlength="8" /><br>
       <span id='pwmessage'></span><br>
    </label>
    <label for="confirmpassword">
      <input type="password" name="confirm_password" id="confirm_password" placeholder=" Confirm password*" required minlength="8" /><br>
      <span id='cpwmessage'></span><br>
    </label>
    <input type="submit" value="submit" onClick="return checkEmpty()" />
</form>

Appreciate it and warm regards!

Answer 2

Give this method a shot! In this scenario, the submission will not go through if either the password or confirm password fields are left empty, or if the confirm password does not match the initial password.

function checkEmpty() {
    if (document.getElementById("password").value == "") {
        document.getElementById("pwmessage").innerHTML = "Please enter at least one character in the password field";
        return false;
    }
    if (document.getElementById("confirm_password").value != document.getElementById("password").value) {
        document.getElementById("cpwmessage").innerHTML = "Kindly verify your password and try again";
        return false;
    };
}

<form novalidate action='process.php' method='get'>
    <label for="password">
       <input type="password" name="password" id="password" placeholder="Password*" required minlength="8" /><br>
       <span id='pwmessage'></span><br>
    </label>
    <label for="confirmpassword">
      <input type="password" name="confirm_password" id="confirm_password" placeholder=" Confirm password*" required minlength="8" /><br>
      <span id='cpwmessage'></span><br>
    </label>
    <input type="submit" value="submit" onClick="return checkEmpty()" />
</form>

Appreciate it and warm regards!

Answer 3

Answer №2

Discover numerous form validation tutorials available to spark your creativity.

This particular version utilizes data attributes and is highly scalable without requiring additional javascript. While more work may be necessary for additional input types, this code is a great starting point.

//Implement validation on blur for each element
document.querySelectorAll("[data-customvalidate] input").forEach(function(element) {
  element.addEventListener("blur", function() {
    validateField(this)
  });
});


//Set up form validation
document.querySelectorAll("[data-customvalidate").forEach(function(element) {
  element.addEventListener("submit", function(event) {
    let isNotValid = false;
    //Iterate through each input element
    this.querySelectorAll("input").forEach(function(input) {
      //Validate the input and set the isNotValid flag
      if (validateField(input) && !isNotValid) {
        isNotValid = true;
      }
    });

    //Prevent form submission if not valid
    if (isNotValid) {    
      event.preventDefault();
    }
  });
});


//Main Validation Function
function validateField(field) {
  let attributes = field.getAttributeNames();
  let parent = field.parentNode
  let errorField = parent.querySelector(".formError");

  let isError = false;
  //Required Validation
  if (attributes.includes("required") && field.value === "") {
    errorField.textContent = `The ${field.dataset.errorfieldname} field is required`;
    isError = true;
    //Min Length Validation
  } else if (attributes.includes("minlength") && (field.value.length < field.getAttribute("minlength"))) {
    errorField.textContent = `The minimum length for ${field.dataset.errorfieldname} field is ${field.getAttribute("minlength")} characters`;
    isError = true;
    //Match Validation
  } else if (attributes.includes("data-mustmatch")) {
    let elementToMatch = document.getElementById(field.dataset.mustmatch);
    if (elementToMatch.value !== field.value) {
      errorField.textContent = `The ${elementToMatch.dataset.errorfieldname} and ${field.dataset.errorfieldname} do not match`;
      isError = true;
    }
  }

  parent.classList.toggle("error", isError);
  return isError;
}

label {
  display: block;
}

label:not(.error)>.formError {
  display: none;
}

label>.formError {
  color: red;
  font-weight: bold;
  padding-left: 1em;
}

<form novalidate data-customvalidate>
  <label for="password">
         <input type="password" name="password" id="password" placeholder="Password*" required minlength="8" data-errorfieldname="Password" />
         <span class="formError"></span>
      </label>
  <label for="confirmpassword">
        <input type="password" name="confirm_password" id="confirm_password" placeholder=" Confirm password*" required minlength="8" data-errorfieldname="Confirm Password" data-mustmatch="password" data-mustmatcherror= "Password and Confirm Password do not match" />
        <span class="formError"></span>
      </label>
  <button>Submit</button>
</form>

Answer 4

Discover numerous form validation tutorials available to spark your creativity.

This particular version utilizes data attributes and is highly scalable without requiring additional javascript. While more work may be necessary for additional input types, this code is a great starting point.

//Implement validation on blur for each element
document.querySelectorAll("[data-customvalidate] input").forEach(function(element) {
  element.addEventListener("blur", function() {
    validateField(this)
  });
});


//Set up form validation
document.querySelectorAll("[data-customvalidate").forEach(function(element) {
  element.addEventListener("submit", function(event) {
    let isNotValid = false;
    //Iterate through each input element
    this.querySelectorAll("input").forEach(function(input) {
      //Validate the input and set the isNotValid flag
      if (validateField(input) && !isNotValid) {
        isNotValid = true;
      }
    });

    //Prevent form submission if not valid
    if (isNotValid) {    
      event.preventDefault();
    }
  });
});


//Main Validation Function
function validateField(field) {
  let attributes = field.getAttributeNames();
  let parent = field.parentNode
  let errorField = parent.querySelector(".formError");

  let isError = false;
  //Required Validation
  if (attributes.includes("required") && field.value === "") {
    errorField.textContent = `The ${field.dataset.errorfieldname} field is required`;
    isError = true;
    //Min Length Validation
  } else if (attributes.includes("minlength") && (field.value.length < field.getAttribute("minlength"))) {
    errorField.textContent = `The minimum length for ${field.dataset.errorfieldname} field is ${field.getAttribute("minlength")} characters`;
    isError = true;
    //Match Validation
  } else if (attributes.includes("data-mustmatch")) {
    let elementToMatch = document.getElementById(field.dataset.mustmatch);
    if (elementToMatch.value !== field.value) {
      errorField.textContent = `The ${elementToMatch.dataset.errorfieldname} and ${field.dataset.errorfieldname} do not match`;
      isError = true;
    }
  }

  parent.classList.toggle("error", isError);
  return isError;
}

label {
  display: block;
}

label:not(.error)>.formError {
  display: none;
}

label>.formError {
  color: red;
  font-weight: bold;
  padding-left: 1em;
}

<form novalidate data-customvalidate>
  <label for="password">
         <input type="password" name="password" id="password" placeholder="Password*" required minlength="8" data-errorfieldname="Password" />
         <span class="formError"></span>
      </label>
  <label for="confirmpassword">
        <input type="password" name="confirm_password" id="confirm_password" placeholder=" Confirm password*" required minlength="8" data-errorfieldname="Confirm Password" data-mustmatch="password" data-mustmatcherror= "Password and Confirm Password do not match" />
        <span class="formError"></span>
      </label>
  <button>Submit</button>
</form>

What is the best way to display an error message for an invalid input using JavaScript?

Answer №1

Answer №2

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