Rent a car: A custom item renderer

The default dropdown item template is just a label. Real applications usually want richer items — a thumbnail, the title, secondary metadata. GolemUI lets you supply a custom item renderer for that.

Step 1 — Enrich the data

The car items now carry an emoji thumbnail and a price:

items: [
  { id: 'compact', label: 'Compact', img: '🚗', price: 35 },
  { id: 'suv', label: 'SUV', img: '🚙', price: 75 },
  { id: 'convertible', label: 'Convertible', img: '🏎️', price: 110 },
  { id: 'luxury', label: 'Luxury', img: '🚘', price: 180 },
],

Step 2 — Implement the renderer

Item renderers are framework-specific components.

React

CarItemRenderer.tsx

import * as React from 'react';
import type { ReactItemRenderer } from '@golemui/react';

type Car = { id: string; label: string; img: string; price: number };

export const CarItemRenderer: ReactItemRenderer<Car> = ({ item }) => (
  <div className="car-item">
    <span className="car-item__img">{item.img}</span>
    <span className="car-item__label">{item.label}</span>
    <span className="car-item__price">${item.price}/day</span>
  </div>
);

Angular

car-item-renderer.component.ts

import { Component } from '@angular/core';
import * as Angular from '@golemui/angular';

type Car = { id: string; label: string; img: string; price: number };

@Component({
  standalone: true,
  selector: 'car-item-renderer',
  template: `
    <div class="car-item">
      <span class="car-item__img">{{ item.img }}</span>
      <span class="car-item__label">{{ item.label }}</span>
      <span class="car-item__price">\${{ item.price }}/day</span>
    </div>
  `,
})
export class CarItemRenderer implements Angular.AngularItemRenderer<Car> {
  item!: Car;
}

Lit

car-item-renderer.element.ts

import { LitElement, html } from 'lit';
import { customElement, property } from 'lit/decorators.js';

type Car = { id: string; label: string; img: string; price: number };

@customElement('car-item-renderer')
export class CarItemRenderer extends LitElement {
  @property({ attribute: false }) item!: Car;

  override createRenderRoot() {
    return this;
  }

  override render() {
    return html`
      <div class="car-item">
        <span class="car-item__img">${this.item.img}</span>
        <span class="car-item__label">${this.item.label}</span>
        <span class="car-item__price">$${this.item.price}/day</span>
      </div>
    `;
  }
}

Step 3 — Add styles

A few lines of CSS to lay the renderer out:

.car-item {
  display: flex;
  align-items: center;
  gap: var(--gui-space-3);
}
.car-item__img { font-size: 1.4em; }
.car-item__label { flex: 1; }
.car-item__price { color: var(--gui-color-fg--secondary); }

Step 4 — Register the renderer

Add it to formConfig.itemRenderers:

const formConfig = {
  itemRenderers: {
    carItemRenderer: CarItemRenderer,
  },
};

Step 5 — Reference it from the dropdown

The dropdown’s itemRenderer prop carries the name you registered:

03-renderer.ts

import { gui } from '@golemui/gui-shared';

export default [
  gui.inputs.dropdown('car', {
    labelField: 'label',
    valueField: 'id',
    itemRenderer: 'carItemRenderer',
    items: [
      {
        id: 'compact',
        label: 'Compact',
        img: '🚗',
        price: 35,
      },
      {
        id: 'suv',
        label: 'SUV',
        img: '🚙',
        price: 75,
      },
      {
        id: 'convertible',
        label: 'Convertible',
        img: '🏎️',
        price: 110,
      },
      {
        id: 'luxury',
        label: 'Luxury',
        img: '🚘',
        price: 180,
      },
    ],
    label: 'Select car',
    validator: {
      type: 'string',
      required: true,
    },
  }),
  gui.inputs.dropdown('collectOffice', {
    labelField: 'label',
    valueField: 'id',
    items: [
      {
        id: 'lhr',
        label: 'London Heathrow',
      },
      {
        id: 'cdg',
        label: 'Paris CDG',
      },
      {
        id: 'fra',
        label: 'Frankfurt Main',
      },
    ],
    label: 'Collect from office',
    validator: {
      type: 'string',
      required: true,
    },
  }),
  gui.inputs.booleanInput('differentReturn', {
    label: 'Choose a different return location',
  }),
  gui.inputs.dropdown('returnOffice', {
    labelField: 'label',
    valueField: 'id',
    items: [
      {
        id: 'lhr',
        label: 'London Heathrow',
      },
      {
        id: 'cdg',
        label: 'Paris CDG',
      },
      {
        id: 'fra',
        label: 'Frankfurt Main',
      },
    ],
    label: 'Return to office',
    validator: {
      type: 'string',
      required: true,
    },
  }),
  gui.inputs.rangeCalendar('rentalDates', {
    label: 'Rental dates',
    validator: {
      type: 'array',
      required: true,
      minItems: 2,
      maxItems: 2,
    },
  }),
  gui.inputs.radiogroup('rentalType', {
    options: [
      {
        label: 'Daily',
        value: 'daily',
      },
      {
        label: 'Weekly',
        value: 'weekly',
      },
      {
        label: 'Monthly',
        value: 'monthly',
      },
    ],
    label: 'Rental type',
    validator: {
      type: 'string',
      required: true,
    },
  }),
  gui.inputs.booleanInput('driverOver25', {
    label: 'Driver aged over 25',
    validator: {
      type: 'boolean',
      const: true,
      required: true,
    },
  }),
  gui.inputs.booleanInput('hasDiscountCode', {
    label: 'I have a discount code',
  }),
  gui.inputs.textInput('discountCode', {
    label: 'Discount code',
    validator: {
      type: 'string',
      required: true,
      minLength: 4,
    },
  }),
  gui.actions.button({
    label: 'Reserve',
    uid: 'submit',
    onClick: 'submit',
  }),
];

03-renderer.json

{
  "states": {
    "differentReturn": "$form.differentReturn === true",
    "hasDiscount": "$form.hasDiscountCode === true"
  },
  "form": [
    {
      "kind": "input",
      "type": "dropdown",
      "path": "car",
      "label": "Select car",
      "validator": { "type": "string", "required": true },
      "props": {
        "labelField": "label",
        "valueField": "id",
        "itemRenderer": "carItemRenderer",
        "items": [
          { "id": "compact", "label": "Compact", "img": "🚗", "price": 35 },
          { "id": "suv", "label": "SUV", "img": "🚙", "price": 75 },
          { "id": "convertible", "label": "Convertible", "img": "🏎️", "price": 110 },
          { "id": "luxury", "label": "Luxury", "img": "🚘", "price": 180 }
        ]
      }
    },
    {
      "kind": "input",
      "type": "dropdown",
      "path": "collectOffice",
      "label": "Collect from office",
      "validator": { "type": "string", "required": true },
      "props": {
        "labelField": "label",
        "valueField": "id",
        "items": [
          { "id": "lhr", "label": "London Heathrow" },
          { "id": "cdg", "label": "Paris CDG" },
          { "id": "fra", "label": "Frankfurt Main" }
        ]
      }
    },
    {
      "kind": "input",
      "type": "toggle",
      "path": "differentReturn",
      "label": "Choose a different return location"
    },
    {
      "kind": "input",
      "type": "dropdown",
      "path": "returnOffice",
      "label": "Return to office",
      "include": { "in": ["differentReturn"] },
      "validator": { "type": "string", "required": true },
      "props": {
        "labelField": "label",
        "valueField": "id",
        "items": [
          { "id": "lhr", "label": "London Heathrow" },
          { "id": "cdg", "label": "Paris CDG" },
          { "id": "fra", "label": "Frankfurt Main" }
        ]
      }
    },
    {
      "kind": "input",
      "type": "rangeCalendar",
      "path": "rentalDates",
      "label": "Rental dates",
      "validator": { "type": "array", "required": true, "minItems": 2, "maxItems": 2 }
    },
    {
      "kind": "input",
      "type": "radiogroup",
      "path": "rentalType",
      "label": "Rental type",
      "validator": { "type": "string", "required": true },
      "props": {
        "options": [
          { "label": "Daily", "value": "daily" },
          { "label": "Weekly", "value": "weekly" },
          { "label": "Monthly", "value": "monthly" }
        ]
      }
    },
    {
      "kind": "input",
      "type": "toggle",
      "path": "driverOver25",
      "label": "Driver aged over 25",
      "validator": { "type": "boolean", "const": true, "required": true }
    },
    {
      "kind": "input",
      "type": "toggle",
      "path": "hasDiscountCode",
      "label": "I have a discount code"
    },
    {
      "kind": "input",
      "type": "textinput",
      "path": "discountCode",
      "label": "Discount code",
      "include": { "in": ["hasDiscount"] },
      "validator": { "type": "string", "required": true, "minLength": 4 }
    },
    {
      "kind": "action",
      "type": "button",
      "label": "Reserve",
      "uid": "submit",
      "on": { "click": "submit" }
    }
  ]
}

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See also

• Features / Item Renderers — wiring renderers in formConfig.
• Extending GolemUI / Item Renderers — the renderer contract per framework.