1 files changed, 69 insertions, 0 deletions
diff --git a/src/data/composite/data/withPropertyFromObject.js b/src/data/composite/data/withPropertyFromObject.js
new file mode 100644
index 0000000..b31bab1
--- /dev/null
+++ b/src/data/composite/data/withPropertyFromObject.js
@@ -0,0 +1,69 @@
+// Gets a property of some object (in a dependency) and provides that value.
+// If the object itself is null, or the object doesn't have the listed property,
+// the provided dependency will also be null.
+//
+// See also:
+//  - withPropertiesFromObject
+//  - withPropertyFromList
+//
+
+import {input, templateCompositeFrom} from '#composite';
+
+export default templateCompositeFrom({
+  annotation: `withPropertyFromObject`,
+
+  inputs: {
+    object: input({type: 'object', acceptsNull: true}),
+    property: input({type: 'string'}),
+  },
+
+  outputs: ({
+    [input.staticDependency('object')]: object,
+    [input.staticValue('property')]: property,
+  }) =>
+    (object && property
+      ? (object.startsWith('#')
+          ? [`${object}.${property}`]
+          : [`#${object}.${property}`])
+      : ['#value']),
+
+  steps: () => [
+    {
+      dependencies: [
+        input.staticDependency('object'),
+        input.staticValue('property'),
+      ],
+
+      compute: (continuation, {
+        [input.staticDependency('object')]: object,
+        [input.staticValue('property')]: property,
+      }) => continuation({
+        '#output':
+          (object && property
+            ? (object.startsWith('#')
+                ? `${object}.${property}`
+                : `#${object}.${property}`)
+            : '#value'),
+      }),
+    },
+
+    {
+      dependencies: [
+        '#output',
+        input('object'),
+        input('property'),
+      ],
+
+      compute: (continuation, {
+        ['#output']: output,
+        [input('object')]: object,
+        [input('property')]: property,
+      }) => continuation({
+        [output]:
+          (object === null
+            ? null
+            : object[property] ?? null),
+      }),
+    },
+  ],
+});