composer require mediawiki/forms dev-REL1_31

wfLoadExtension( 'Forms' );

{
    title: "Request vacation",
    target: {
        type: 'email', //May also be 'templates-on-wikipage', which is default and takes other parameters
        receivers: [ 'serverside-configured-receiver-1', 'serverside-configured-receiver-2' ]
    },
    items: [
        {
            type: 'panel',
            html: 'This is the vacation registration from. Please fill in the required information and submit it.'
        },
        {
            type: 'currentuser' //Hidden by default
        },
        {
            type: 'fieldset',
            name: 'dates', //When writing templates to a wiki page, this could be the target template name
            layout: 'hbox',
            items: [
                {
                    type: 'datepicker',
                    name: 'from',
                    fielLabel: 'Begin'
                },
                {
                    type: 'datepicker',
                    name: 'end',
                    fielLabel: 'End',
                    //Even better would be a dedicated field type "daterangepicker" that incorporates two 'datepicker' and wires them up automatically
                    getStart: function( form ) {
                        return form.getField( 'from' ).getValue();
                    }
                }
            ]
        },
        {
            type: 'textarea',
            name: 'notes',
            fieldLabel: 'Notes',
            labelAlign: 'top'
        }
    ]
}