Starting to mess with promises

Going to want async IO, I think. And it's a fun detail that I guess
I'm in charge of deciding when to run promise completion functions. :D

oden-js/src/promise.rs

@@ -0,0 +1,34 @@
+use crate::{ContextRef, Value, ValueRef};
+
+#[derive(Debug, Clone)]
+pub struct Promise {
+    pub object: Value,
+    pub resolve_fn: Value,
+    pub reject_fn: Value,
+}
+
+impl Promise {
+    pub(crate) fn new(object: Value, resolve_fn: Value, reject_fn: Value) -> Self {
+        Promise {
+            object,
+            resolve_fn,
+            reject_fn,
+        }
+    }
+
+    pub fn dup(&self, ctx: &ContextRef) -> Self {
+        Promise {
+            object: self.object.dup(ctx),
+            resolve_fn: self.resolve_fn.dup(ctx),
+            reject_fn: self.reject_fn.dup(ctx),
+        }
+    }
+
+    pub fn resolve(self, context: &ContextRef, value: &ValueRef) {
+        let _ = self.resolve_fn.call(context, &[value]);
+    }
+
+    pub fn reject(self, context: &ContextRef, value: &ValueRef) {
+        let _ = self.reject_fn.call(context, &[value]);
+    }
+}