added script-loading extension primitive

HISTORY.md

@@ -9,7 +9,10 @@
 * **Notable Fixes:**
     * fixed occasional invisible error messages
 
-### 2021-06-19
+### 2021-06-22
+* extensions: added script-loading extension primitive
+
+### 2021-06-20
 * updated extensions documentation
 
 ### 2021-06-19

snap.html

@@ -19,7 +19,7 @@
         <script src="src/sketch.js?version=2020-07-13"></script>
         <script src="src/video.js?version=2019-06-27"></script>
         <script src="src/maps.js?version=2021-06-15"></script>
-        <script src="src/extensions.js?version=2021-06-20"></script>
+        <script src="src/extensions.js?version=2021-06-22"></script>
         <script src="src/xml.js?version=2020-04-27"></script>
         <script src="src/store.js?version=2021-06-10"></script>
         <script src="src/locale.js?version=2021-06-11"></script>

src/extensions.js

@@ -31,13 +31,14 @@
 IDE_Morph, CamSnapshotDialogMorph, SoundRecorderDialogMorph, isSnapObject, nop,
 Color, contains*/
 
-modules.extensions = '2021-June-20';
+modules.extensions = '2021-June-22';
 
 // Global stuff
 
 var SnapExtensions = {
     primitives: new Map(),
-    menus: new Map()
+    menus: new Map(),
+    scripts: []
 };
 
 /*
@@ -108,6 +109,8 @@ var SnapExtensions = {
     Whatever you do, please use these extension capabilities sensibly.
 */
 
+// Primitives
+
 // errors & exceptions (err_):
 
 SnapExtensions.primitives.set(
@@ -674,6 +677,17 @@ SnapExtensions.primitives.set(
     }
 );
 
+// loading external scripts (scr_)
+
+SnapExtensions.primitives.set(
+    'scr_load(url)',
+    function (url) {
+        return SnapExtensions.loadScript(url);
+    }
+);
+
+// Menus
+
 SnapExtensions.menus.set(
     'clr_numbers', // Brian's browns and oranges, sigh...
     function () {
@@ -900,3 +914,22 @@ SnapExtensions.menus.set(
         }
     }
 );
+
+// Scripts
+
+SnapExtensions.loadScript = function (url) {
+    var scriptElement,
+        isLoaded = false;
+
+    if (contains(this.scripts, url)) {
+        return () => true;
+    }
+    scriptElement = document.createElement('script');
+    scriptElement.onload = () => {
+        this.scripts.push(url);
+        isLoaded = true;
+    };
+    document.head.appendChild(scriptElement);
+    scriptElement.src = url;
+    return () => isLoaded;
+};