Conditional Form Fields (States)

Doc : https://www.drupal.org/docs/drupal-apis/form-api/conditional-form-fields

States that can be applied to a form field element:

• enabled
• disabled
• required
• optional
• visible
• invisible
• checked
• unchecked
• expanded
• collapsed
  
   

The following states may be used when checking values of other fields:

• empty
• filled
• checked
• unchecked
• expanded
• collapsed
• value
  
   

The following states exist for both elements and remote conditions. 

Those might not be implemented in all browsers and may not change anything on the element:

• relevant
• irrelevant
• valid
• invalid
• touched
• untouched
• readwrite
• readonly

Examples :

Disable submit button until email field is empty

$form['submit'] = [

'#type' => 'submit',

  '#states' => [

    'disabled' => [':input[name="email"]' => ['value' => ''],]

  ]

];

OR, AND, XOR Conditions

'disabled' => [

  [':input[name="email"]' => ['value' => ''],],

  'and',

  [':input[name="zip_code"]' => ['value' => ''],],

]