add a polyfill for Promise.withResolvers

I'd forgotten to check its compatibility, and it's slightly newer than I'd like.

This adds a polyfill at the top of numbas.js, so it can be used on browsers that don't have it built in.

The polyfill can be removed once it's widely supported.

Author: christianp

runtime/scripts/numbas.js

@@ -25,6 +25,18 @@ Copyright 2011-14 Newcastle University
         _globalThis.Numbas = {}
     }
 
+// Polyfill for Promise.withResolvers. Remove once it's reached 95% compatibility.
+if(!Promise.withResolvers) {
+    Promise.withResolvers = function() {
+        const out = {};
+        out.promise = new this((resolve, reject) => {
+            out.resolve = resolve;
+            out.reject = reject;
+        });
+        return out;
+    }
+}
+
 /** @namespace Numbas */
 /** Extensions should add objects to this so they can be accessed */
 Numbas.extensions = {};

tests/jme-runtime.js

@@ -27,6 +27,18 @@ Copyright 2011-14 Newcastle University
         _globalThis.Numbas = {}
     }
 
+// Polyfill for Promise.withResolvers. Remove once it's reached 95% compatibility.
+if(!Promise.withResolvers) {
+    Promise.withResolvers = function() {
+        const out = {};
+        out.promise = new this((resolve, reject) => {
+            out.resolve = resolve;
+            out.reject = reject;
+        });
+        return out;
+    }
+}
+
 /** @namespace Numbas */
 /** Extensions should add objects to this so they can be accessed */
 Numbas.extensions = {};

tests/numbas-runtime.js

@@ -28,6 +28,18 @@ Copyright 2011-14 Newcastle University
         _globalThis.Numbas = {}
     }
 
+// Polyfill for Promise.withResolvers. Remove once it's reached 95% compatibility.
+if(!Promise.withResolvers) {
+    Promise.withResolvers = function() {
+        const out = {};
+        out.promise = new this((resolve, reject) => {
+            out.resolve = resolve;
+            out.reject = reject;
+        });
+        return out;
+    }
+}
+
 /** @namespace Numbas */
 /** Extensions should add objects to this so they can be accessed */
 Numbas.extensions = {};