1 files changed, 80 insertions, 0 deletions
diff --git a/toolkit/content/widgets/moz-button-group/moz-button-group.mjs b/toolkit/content/widgets/moz-button-group/moz-button-group.mjs
new file mode 100644
index 0000000000..1fc27624f4
--- /dev/null
+++ b/toolkit/content/widgets/moz-button-group/moz-button-group.mjs
@@ -0,0 +1,80 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+import { html } from "../vendor/lit.all.mjs";
+import { MozLitElement } from "../lit-utils.mjs";
+
+export const PLATFORM_LINUX = "linux";
+export const PLATFORM_MACOS = "macosx";
+export const PLATFORM_WINDOWS = "win";
+
+export default class MozButtonGroup extends MozLitElement {
+  static queries = {
+    defaultSlotEl: "slot:not([name])",
+    primarySlotEl: "slot[name=primary]",
+  };
+
+  static properties = {
+    platform: { state: true },
+  };
+
+  // Use a relative URL in storybook to get faster reloads on style changes.
+  static stylesheetUrl = window.IS_STORYBOOK
+    ? "./moz-button-group/moz-button-group.css"
+    : "chrome://global/content/elements/moz-button-group.css";
+
+  constructor() {
+    super();
+    this.#detectPlatform();
+  }
+
+  #detectPlatform() {
+    if (typeof AppConstants !== "undefined") {
+      this.platform = AppConstants.platform;
+    } else if (navigator.platform.includes("Linux")) {
+      this.platform = PLATFORM_LINUX;
+    } else if (navigator.platform.includes("Mac")) {
+      this.platform = PLATFORM_MACOS;
+    } else {
+      this.platform = PLATFORM_WINDOWS;
+    }
+  }
+
+  onSlotchange(e) {
+    for (let child of this.defaultSlotEl.assignedNodes()) {
+      if (!(child instanceof Element)) {
+        // Text nodes won't support classList or getAttribute.
+        continue;
+      }
+      // Bug 1791816: These should check moz-button instead of button.
+      if (
+        child.localName == "button" &&
+        (child.classList.contains("primary") ||
+          child.getAttribute("type") == "submit" ||
+          child.hasAttribute("autofocus"))
+      ) {
+        child.slot = "primary";
+      }
+    }
+  }
+
+  render() {
+    let slots = [
+      html`
+        <slot @slotchange=${this.onSlotchange}></slot>
+      `,
+      html`
+        <slot name="primary"></slot>
+      `,
+    ];
+    if (this.platform == PLATFORM_WINDOWS) {
+      slots = [slots[1], slots[0]];
+    }
+    return html`
+      <link rel="stylesheet" href=${this.constructor.stylesheetUrl} />
+      ${slots}
+    `;
+  }
+}
+customElements.define("moz-button-group", MozButtonGroup);