Add user-defined components how-to (#1557)

* Add user-defined components how-to

* Properly indent code samples in list

* link from JSX component page to user-defined components page

* Remove Button from Insight tsx component

* from > to

* Fix Address example

* use valid ethereum addresses in examples

* add a section on spreading props

* edit content

---------

Co-authored-by: Alexandra Tran <alexandratran@protonmail.com>

Author: ziad-saab

snaps/features/custom-ui/user-defined-components.md

@@ -0,0 +1,258 @@
+---
+description: Create your own JSX components to improve readability.
+sidebar_position: 5
+---
+
+# User-defined components
+
+When using [Custom UI with JSX](with-jsx.md), you can create your own components by composing
+existing components or other user-defined components.
+
+## Basic example
+
+In this first, basic example, the user-defined component is static.
+It does not accept any props (parameters) and returns the contents of a static home page.
+
+```jsx title="Home.jsx"
+import { Box, Heading, Text } from "@metamask/snaps-sdk/jsx";
+
+export const Home = () => {
+  return (
+    <Box>
+      <Heading>Welcome to my Snap</Heading>
+      <Text>Hello, world!</Text>
+    </Box>
+  );
+};
+```
+
+Once the component is defined, you can use it anywhere in the Snap.
+For example, to display the home page, you can use the following code:
+
+```jsx title="index.jsx"
+import { Home } from "./Home";
+
+export const onHomepage = () => {
+  return <Home />;
+};
+```
+
+## Example with props
+
+You can parameterize components by passing props.
+Props are passed to the component as an object and can be accessed using the first parameter of the
+component's definition function:
+
+```jsx title="Insight.jsx"
+export const Insight = (props) => {
+  return (
+    <Box>
+      <Row label="From">
+        <Address address={props.from} />
+      </Row>
+      <Row label="To">
+        {to ? <Address address={props.to} /> : <Text>None</Text>}
+      </Row>
+    </Box>
+  );
+};
+```
+
+This example contains two usages of props:
+
+- The `Insight` component accepts a `props` parameter, which is an object containing the `from` and
+  `to` addresses.
+  The `from` address is accessed using `props.from`, and the `to` address is accessed using
+  `props.to`, since `props` is just a regular JavaScript object.
+- The `Insight` component then uses the built-in `Address` component to display addresses.
+  The `Address` component accepts an `address` prop.
+  When using the `Address` component, you can pass props to it using a notation similar to HTML
+  attributes: `address={props.from}`.
+
+To use the `Insight` component, you can pass the `from` and `to` addresses as props:
+
+```jsx title="index.jsx"
+import { Insight } from "./Insight";
+
+export const onTransaction = ({ transaction }) => {
+  return { content: <Insight from={transaction.from} to={transaction.to} /> };
+};
+```
+
+You can also access props using destructuring.
+This is not specific to JSX, but a feature of JavaScript:
+
+```jsx title="Insight.jsx"
+export const Insight = ({ from, to }) => {
+  return (
+    <Box>
+      <Row label="From">
+        <Address address={from} />
+      </Row>
+      <Row label="To">
+        {to ? <Address address={to} /> : <Text>None</Text>}
+      </Row>
+    </Box>
+  );
+};
+```
+
+## Return multiple elements
+
+A JSX expression can only contain a single root element.
+To return multiple elements, wrap them in a parent element, such as `Box`.
+In the previous example, the two `Row` elements are wrapped in a `Box` element.
+Trying to return multiple elements without a parent element results in a syntax error:
+
+```jsx title="WRONG-Insight.jsx"
+export const Insight = ({ from, to }) => {
+
+  // This causes a syntax error
+  return (
+    <Row label="From">
+      <Address address={from} />
+    </Row>
+    <Row label="To">
+      {to ? <Address address={to} /> : <Text>None</Text>}
+    </Row>
+  );
+};
+```
+
+## Return a list
+
+To return a list of elements, you can use an array.
+In the following example, the `Accounts` components receives an array of accounts as props, and uses
+the array to display a list of accounts using `Array.map`:
+
+```jsx title="Accounts.jsx"
+export const Accounts = ({ accounts }) => {
+  return (
+    <Box>
+      <Heading>Accounts</Heading>
+      {accounts.map((account) => (
+        <Row label={account.name}>
+          <Address address={account.address} />
+        </Row>
+      ))}
+    </Box>
+  );
+};
+```
+
+To use the `Accounts` component, you can pass an array of accounts as props:
+
+```jsx title="index.jsx"
+import { Accounts } from "./Accounts";
+
+export const onHomepage = () => {
+  const accounts = [
+    {
+      name: "Account 1",
+      address: "0x6827b8f6cc60497d9bf5210d602C0EcaFDF7C405"
+    },
+    {
+      name: "Account 2",
+      address: "0x71C7656EC7ab88b098defB751B7401B5f6d8976F"
+    }
+  ];
+  return <Accounts accounts={accounts} />;
+};
+```
+
+## Spread props
+
+If an object has the same keys and value types as the props of a component, you can spread the
+object's properties as props for the component.
+For example, given the following component:
+
+```jsx title="Account.jsx"
+export const Account = ({ name, address }) => {
+  return <Row label={name}>
+    <Address address={address} />
+  </Row>
+};
+```
+
+Instead of writing:
+
+```jsx title="index.jsx"
+const myAccount = {
+  name: "Account 1",
+  address: "0x6827b8f6cc60497d9bf5210d602C0EcaFDF7C405"
+};
+
+// ...
+return <Account name={myAccount.name} address={myAccount.address} />
+```
+
+You can write:
+
+```jsx
+return <Account {...myAccount} />
+```
+
+## Use with TypeScript
+
+The `@metamask/snaps-sdk/jsx` package exports a `SnapComponent` type that you can use to define
+components that are compatible with TypeScript.
+The `SnapComponent` type is generic: it accepts a `Props` type parameter that defines the shape of
+the props object.
+For example:
+
+```tsx title="Insight.tsx"
+import type { SnapComponent } from "@metamask/snaps-sdk/jsx";
+import { Button, Box, Text, Row, Address } from "@metamask/snaps-sdk/jsx";
+
+type InsightProps = {
+  from: string;
+  to?: string;
+};
+
+export const Insight: SnapComponent<InsightProps> = ({ from, to }) => {
+  return (
+    <Box>
+      <Row label="From">
+        <Address address={from as `0x${string}`} />
+      </Row>
+      <Row label="To">
+        {to ? <Address address={to as `0x${string}`} /> : <Text>None</Text>}
+      </Row>
+    </Box>
+  );
+};
+```
+
+Use the following steps to create user-defined components with TypeScript:
+
+1. Import the `SnapComponent` type:
+
+   ```tsx
+   import type { SnapComponent } from "@metamask/snaps-sdk/jsx";
+   ```
+
+2. Define a type for the props of your component.
+   For example:
+
+   ```tsx
+   type InsightProps = {
+     from: string;
+     to?: string;
+   };
+   ```
+
+3. Annotate the type of your component.
+   For example:
+
+   ```tsx
+   export const Insight: SnapComponent<InsightProps> = ({ from, to }) => {
+     // ...
+   };
+   ```
+
+   This has two effects:
+   
+   - It allows TypeScript to infer the types of the props inside your component.
+   - It ensures that the props passed to the component match the expected props.
+     In this example, using the `Insight` component without the `from` prop, or passing a `number`
+     instead of a `string` for the `from` prop results in a type error.

snaps/features/custom-ui/with-jsx.md

@@ -712,7 +712,7 @@ module.exports.onHomePage = async () => {
 <img src={require("../../assets/custom-ui-heading.png").default} alt="Text UI example" width="450px" style={{border: "1px solid #DCDCDC"}} />
 </p>
 
-## Emojis
+### Emojis
 
 Text-based components (such as [`Heading`](#heading) and [`Text`](#text)) accept emojis.
 
@@ -738,3 +738,7 @@ await snap.request({
 <p align="center">
 <img src={require("../../assets/custom-ui-emojis.png").default} alt="Emojis UI example" width="450px" style={{border: "1px solid #DCDCDC"}} />
 </p>
+
+## User-defined components
+
+In addition to the components provided by the SDK, you can [define your own components](user-defined-components.md).