Implement breakpointObserver.

Drop breakpoints constant export from Breakpoint component.
Expose breakpoints constant separately and freeze it.
Change `match` event to 'change`, because it is now based on store and captures initial value change.

Issues:
- Wrong exports in types/index.d.ts
- Typedefs lost from docs.

COMPONENT_INDEX.md

@@ -348,21 +348,12 @@ None.
 
 ## `Breakpoint`
 
-### Types
-
-```ts
-export type BreakpointSize = "sm" | "md" | "lg" | "xlg" | "max";
-
-export type BreakpointValue = 320 | 672 | 1056 | 1312 | 1584;
-```
-
 ### Props
 
 | Prop name | Kind             | Reactive | Type                                         | Default value                                                             | Description                                       |
-| :---------- | :----------------- | :------- | :--------------------------------------------------- | ------------------------------------------------------------------------- | ------------------------------------------------- |
+| :-------- | :--------------- | :------- | :------------------------------------------- | ------------------------------------------------------------------------- | ------------------------------------------------- |
 | sizes     | <code>let</code> | Yes      | <code>Record<BreakpointSize, boolean></code> | <code>{ sm: false, md: false, lg: false, xlg: false, max: false, }</code> | Carbon grid sizes as an object                    |
 | size      | <code>let</code> | Yes      | <code>BreakpointSize</code>                  | <code>undefined</code>                                                    | Determine the current Carbon grid breakpoint size |
-| breakpoints | <code>const</code> | No       | <code>Record<BreakpointSize, BreakpointValue></code> | <code>{ sm: 320, md: 672, lg: 1056, xlg: 1312, max: 1584, }</code>        | Reference the Carbon grid breakpoints             |
 
 ### Slots
 
@@ -374,7 +365,7 @@ export type BreakpointValue = 320 | 672 | 1056 | 1312 | 1584;
 
 | Event name | Type       | Detail                                                                   |
 | :--------- | :--------- | :----------------------------------------------------------------------- |
-| match      | dispatched | <code>{ size: BreakpointSize; breakpointValue: BreakpointValue; }</code> |
+| change     | dispatched | <code>{ size: BreakpointSize; breakpointValue: BreakpointValue; }</code> |
 
 ## `Button`
 

docs/src/COMPONENT_API.json

@@ -387,17 +387,6 @@
           "isFunctionDeclaration": false,
           "constant": false,
           "reactive": true
-        },
-        {
-          "name": "breakpoints",
-          "kind": "const",
-          "description": "Reference the Carbon grid breakpoints",
-          "type": "Record<BreakpointSize, BreakpointValue>",
-          "value": "{     sm: 320,     md: 672,     lg: 1056,     xlg: 1312,     max: 1584,   }",
-          "isFunction": false,
-          "isFunctionDeclaration": false,
-          "constant": true,
-          "reactive": false
         }
       ],
       "slots": [
@@ -410,22 +399,11 @@
       "events": [
         {
           "type": "dispatched",
-          "name": "match",
+          "name": "change",
           "detail": "{ size: BreakpointSize; breakpointValue: BreakpointValue; }"
         }
       ],
-      "typedefs": [
-        {
-          "type": "\"sm\" | \"md\" | \"lg\" | \"xlg\" | \"max\"",
-          "name": "BreakpointSize",
-          "ts": "type BreakpointSize = \"sm\" | \"md\" | \"lg\" | \"xlg\" | \"max\""
-        },
-        {
-          "type": "320 | 672 | 1056 | 1312 | 1584",
-          "name": "BreakpointValue",
-          "ts": "type BreakpointValue = 320 | 672 | 1056 | 1312 | 1584"
-        }
-      ]
+      "typedefs": []
     },
     {
       "moduleName": "Button",

src/Breakpoint/Breakpoint.svelte

@@ -1,8 +1,6 @@
 <script>
   /**
-   * @typedef {"sm" | "md" | "lg" | "xlg" | "max"} BreakpointSize
-   * @typedef {320 | 672 | 1056 | 1312 | 1584} BreakpointValue
-   * @event {{ size: BreakpointSize; breakpointValue: BreakpointValue; }} match
+   * @event {{ size: BreakpointSize; breakpointValue: BreakpointValue; }} change
    * @slot {{ size: BreakpointSize; sizes: Record<BreakpointSize, boolean>; }}
    */
 
@@ -24,77 +22,23 @@
     max: false,
   };
 
-  /**
-   * Reference the Carbon grid breakpoints
-   * @type {Record<BreakpointSize, BreakpointValue>}
-   */
-  export const breakpoints = {
-    sm: 320,
-    md: 672,
-    lg: 1056,
-    xlg: 1312,
-    max: 1584,
-  };
-
-  import { createEventDispatcher, onMount } from "svelte";
+  import { createEventDispatcher } from "svelte";
+  import { breakpointObserver } from "./breakpointObserver";
+  import { breakpoints } from "./constants";
 
   const dispatch = createEventDispatcher();
+  const observer = breakpointObserver();
 
-  onMount(() => {
-    const width = window.innerWidth;
-
-    if (width > breakpoints.max) size = "max";
-    else if (width < breakpoints.md) size = "sm";
-    else if (width >= breakpoints.md && width <= breakpoints.lg) size = "md";
-    else if (width >= breakpoints.lg && width <= breakpoints.xlg) size = "lg";
-    else if (width >= breakpoints.xlg && width <= breakpoints.max) size = "xlg";
-
-    const match = {
-      sm: window.matchMedia(`(max-width: ${breakpoints.md}px)`),
-      md: window.matchMedia(
-        `(min-width: ${breakpoints.md}px) and (max-width: ${breakpoints.lg}px)`
-      ),
-      lg: window.matchMedia(
-        `(min-width: ${breakpoints.lg}px) and (max-width: ${breakpoints.xlg}px)`
-      ),
-      xlg: window.matchMedia(
-        `(min-width: ${breakpoints.xlg}px) and (max-width: ${breakpoints.max}px)`
-      ),
-      max: window.matchMedia(`(min-width: ${breakpoints.max}px)`),
+  $: size = $observer;
+  $: sizes = {
+    sm: size == "sm",
+    md: size == "md",
+    lg: size == "lg",
+    xlg: size == "xlg",
+    max: size == "max",
   };
-    const matchers = Object.entries(match);
-    const matchersBySize = Object.fromEntries(
-      matchers.map(([size, queryList]) => [queryList.media, size])
-    );
-
-    function handleChange({ matches, media }) {
-      const size = matchersBySize[media];
-
-      sizes = { ...sizes };
-      sizes[size] = matches;
-
-      if (matches)
-        dispatch("match", { size, breakpointValue: breakpoints[size] });
-    }
-
-    matchers.forEach(([size, queryList]) =>
-      queryList.addEventListener("change", handleChange)
-    );
-
-    return () => {
-      matchers.forEach(([size, queryList]) =>
-        queryList.removeEventListener("change", handleChange)
-      );
-    };
-  });
-
-  $: {
-    if (sizes.sm) size = "sm";
-    if (sizes.md) size = "md";
-    if (sizes.lg) size = "lg";
-    if (sizes.xlg) size = "xlg";
-    if (sizes.max) size = "max";
-  }
+  $: if (size != undefined)
+    dispatch("change", { size, breakpointValue: breakpoints[size] });
 </script>
 
 <slot size="{size}" sizes="{sizes}" />

src/Breakpoint/breakpointObserver.js

@@ -0,0 +1,71 @@
+/// <reference path="./types.d.ts"/>
+
+import { onMount } from "svelte";
+import { derived, writable } from "svelte/store";
+import { breakpoints } from "./constants";
+
+/**
+ * Creates a readable store that returns the current {@link BreakpointSize}.
+ * It also provides functions for creating derived stores used to do comparisons.
+ */
+export function breakpointObserver() {
+  const store = writable(undefined);
+
+  onMount(() => {
+    /** @type {Record<BreakpointSize, MediaQueryList>} */
+    const match = {
+      sm: window.matchMedia(`(max-width: ${breakpoints.md}px)`),
+      md: window.matchMedia(
+        `(min-width: ${breakpoints.md}px) and (max-width: ${breakpoints.lg}px)`
+      ),
+      lg: window.matchMedia(
+        `(min-width: ${breakpoints.lg}px) and (max-width: ${breakpoints.xlg}px)`
+      ),
+      xlg: window.matchMedia(
+        `(min-width: ${breakpoints.xlg}px) and (max-width: ${breakpoints.max}px)`
+      ),
+      max: window.matchMedia(`(min-width: ${breakpoints.max}px)`),
+    };
+    const matchers = Object.entries(match);
+    const sizeByMedia = Object.fromEntries(
+      matchers.map(([size, queryList]) => [queryList.media, size])
+    );
+
+    const size = matchers.find(([size, queryList]) => queryList.matches)[0];
+    store.set(size);
+
+    /** @type {(e: MediaQueryListEvent) => void} */
+    function handleChange({ matches, media }) {
+      const size = sizeByMedia[media];
+      if (matches) store.set(size);
+    }
+
+    matchers.forEach(([size, queryList]) =>
+      queryList.addEventListener("change", handleChange)
+    );
+
+    return () => {
+      matchers.forEach(([size, queryList]) =>
+        queryList.removeEventListener("change", handleChange)
+      );
+    };
+  });
+
+  return {
+    subscribe: store.subscribe,
+    /**
+     * Returns a store readable store that returns whether the current
+     * breakpoint smaller than {@link size}.
+     * @param {BreakpointSize} size Size to compare against.
+     */
+    smallerThan: (size) =>
+      derived(store, ($size) => breakpoints[$size] < breakpoints[size]),
+    /**
+     * Returns a store readable store that returns whether the current
+     * breakpoint larger than {@link size}.
+     * @param {BreakpointSize} size Size to compare against.
+     */
+    largerThan: (size) =>
+      derived(store, ($size) => breakpoints[$size] > breakpoints[size]),
+  };
+}

src/Breakpoint/constants.js

@@ -0,0 +1,13 @@
+/// <reference path="./types.d.ts"/>
+
+/**
+ * Pixel sizes of Carbon grid breakpoints.
+ * @type {Record<BreakpointSize, BreakpointValue>}
+ */
+export const breakpoints = Object.freeze({
+  sm: 320,
+  md: 672,
+  lg: 1056,
+  xlg: 1312,
+  max: 1584,
+});

src/Breakpoint/index.js

@@ -1 +1,3 @@
 export { default as Breakpoint } from "./Breakpoint.svelte";
+export { breakpointObserver } from "./breakpointObserver";
+export { breakpoints } from "./constants";

src/Breakpoint/types.d.ts

@@ -0,0 +1,2 @@
+declare type BreakpointSize = "sm" | "md" | "lg" | "xlg" | "max";
+declare type BreakpointValue = 320 | 672 | 1056 | 1312 | 1584;

src/index.js

@@ -1,7 +1,7 @@
 export { Accordion, AccordionItem, AccordionSkeleton } from "./Accordion";
 export { AspectRatio } from "./AspectRatio";
 export { Breadcrumb, BreadcrumbItem, BreadcrumbSkeleton } from "./Breadcrumb";
-export { Breakpoint } from "./Breakpoint";
+export { Breakpoint, breakpoints, breakpointObserver } from "./Breakpoint";
 export { Button, ButtonSkeleton, ButtonSet } from "./Button";
 export { Checkbox, CheckboxSkeleton } from "./Checkbox";
 export { ContentSwitcher, Switch } from "./ContentSwitcher";

types/Breakpoint/Breakpoint.svelte.d.ts

@@ -1,10 +1,6 @@
 /// <reference types="svelte" />
 import { SvelteComponentTyped } from "svelte";
 
-export type BreakpointSize = "sm" | "md" | "lg" | "xlg" | "max";
-
-export type BreakpointValue = 320 | 672 | 1056 | 1312 | 1584;
-
 export interface BreakpointProps {
   /**
    * Determine the current Carbon grid breakpoint size
@@ -22,15 +18,10 @@ export interface BreakpointProps {
 export default class Breakpoint extends SvelteComponentTyped<
   BreakpointProps,
   {
-    match: CustomEvent<{
+    change: CustomEvent<{
       size: BreakpointSize;
       breakpointValue: BreakpointValue;
     }>;
   },
   { default: { size: BreakpointSize; sizes: Record<BreakpointSize, boolean> } }
-> {
-  /**
-   * Reference the Carbon grid breakpoints
-   */
-  breakpoints: Record<BreakpointSize, BreakpointValue>;
-}
+> {}

types/index.d.ts

@@ -6,6 +6,8 @@ export { default as Breadcrumb } from "./Breadcrumb/Breadcrumb.svelte";
 export { default as BreadcrumbItem } from "./Breadcrumb/BreadcrumbItem.svelte";
 export { default as BreadcrumbSkeleton } from "./Breadcrumb/BreadcrumbSkeleton.svelte";
 export { default as Breakpoint } from "./Breakpoint/Breakpoint.svelte";
+export { default as breakpoints } from "./Breakpoint";
+export { default as breakpointObserver } from "./Breakpoint";
 export { default as Button } from "./Button/Button.svelte";
 export { default as ButtonSkeleton } from "./Button/ButtonSkeleton.svelte";
 export { default as ButtonSet } from "./Button/ButtonSet.svelte";