contact-form.js

[].slice.call( document.querySelectorAll( '.input' ) ).forEach( function( inputEl ) {
    // in case the input is already filled..
    if( inputEl.value.trim() !== '' ) {
        classie.add( inputEl.parentNode, 'input--filled' );
    }

    // events:
    inputEl.addEventListener( 'focus', onInputFocus );
    inputEl.addEventListener( 'blur', onInputBlur );
} );

function onInputFocus( ev ) {
      classie.add( ev.target.parentNode, 'input--filled' );
}

function onInputBlur( ev ) {
      if( ev.target.value.trim() === '' ) {
            classie.remove( ev.target.parentNode, 'input--filled' );
      }
}