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JavaScript Basic Form Validation

Client-side form validation example using JavaScript to check for required fields and valid email format before allowing submission. Provides instant feedback to users.

295

#javascript

#form

#validation

#client-side

#required field

#email validation

/HTML *CSS ()JS Output Live Updates

:root {
  --error: #ef4444;
  --success: #22c55e;
  --primary: #6366f1;
}

* {
  font-family: system-ui, "Segoe UI", Roboto, Helvetica, Arial, sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol";
  box-sizing: border-box;
}

.form-card {
  max-width: 400px;
  margin: 40px auto;
  padding: 30px;
  background: white;
  border-radius: 20px;
  box-shadow: 0 10px 25px rgba(0,0,0,0.05);
}

.input-field {
  position: relative;
  margin-bottom: 25px;
}

/* Floating Label Logic */
.input-field input {
  width: 100%;
  padding: 12px 0;
  border: none;
  border-bottom: 2px solid #e2e8f0;
  font-size: 1rem;
  outline: none;
  transition: all 0.3s ease;
}

.input-field label {
  position: absolute;
  top: 12px;
  left: 0;
  color: #94a3b8;
  pointer-events: none;
  transition: all 0.3s ease;
}

.input-field input:focus ~ label,
.input-field input:not(:placeholder-shown) ~ label {
  top: -12px;
  font-size: 0.8rem;
  font-weight: 700;
  color: var(--primary);
}

.input-field input:focus {
  border-color: var(--primary);
}

/* Validation States */
.input-field.invalid input { border-color: var(--error); }
.input-field.invalid label { color: var(--error); }

.error-hint {
  font-size: 0.75rem;
  color: var(--error);
  position: absolute;
  bottom: -18px;
  left: 0;
  opacity: 0;
  transform: translateY(-5px);
  transition: all 0.2s ease;
}

.input-field.invalid .error-hint {
  opacity: 1;
  transform: translateY(0);
}

button {
  width: 100%;
  padding: 14px;
  border-radius: 12px;
  border: none;
  background: var(--primary);
  color: white;
  font-weight: 600;
  cursor: pointer;
  transition: transform 0.2s;
}

button:active { transform: scale(0.98); }

const form = document.getElementById('myForm');
const inputs = form.querySelectorAll('input');

// Real-time validation
inputs.forEach(input => {
  input.addEventListener('blur', () => validateInput(input));
  input.addEventListener('input', () => {
    if (input.parentElement.classList.contains('invalid')) {
      validateInput(input);
    }
  });
});

form.addEventListener('submit', (e) => {
  e.preventDefault();
  
  // Validate all inputs before submit
  let isFormValid = true;
  inputs.forEach(input => {
    validateInput(input);
    if (!input.validity.valid) isFormValid = false;
  });

if (isFormValid) {
    const btn = form.querySelector('button');
    btn.innerText = 'Success! ✓';
    btn.style.backgroundColor = 'var(--success)';
    console.log('FormData:', Object.fromEntries(new FormData(form)));
  }
});

JavaScript Basic Form Validation

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