Initial PromiseScheduler implementation

Author: kateinoigakukun

ext/js/lib/js.rb

@@ -15,6 +15,57 @@
 module JS
   Undefined = JS.eval("return undefined")
   Null = JS.eval("return null")
+
+  def self.promise_scheduler
+    @promise_scheduler
+  end
+
+  def self.eval_async(code, future)
+    @promise_scheduler ||= PromiseScheduler.new Fiber.current
+    Fiber.new do
+      future.resolve JS::Object.wrap(Kernel.eval(code.to_s, nil, "eval_async"))
+    rescue => e
+      future.reject JS::Object.wrap(e)
+    end.transfer
+  end
+
+  class PromiseScheduler
+    Task = Struct.new(:fiber, :status, :value)
+
+    def initialize(main_fiber)
+      @tasks = []
+      @is_spinning = false
+      @loop_fiber = Fiber.new do
+        loop do
+          while task = @tasks.shift
+            task.fiber.transfer(task.value, task.status)
+          end
+          @is_spinning = false
+          main_fiber.transfer
+        end
+      end
+    end
+
+    def await(promise)
+      current = Fiber.current
+      promise.call(
+        :then,
+        ->(value) { enqueue Task.new(current, :success, value) },
+        ->(value) { enqueue Task.new(current, :failure, value) }
+      )
+      value, status = @loop_fiber.transfer
+      raise JS::Error.new(value) if status == :failure
+      value
+    end
+
+    def enqueue(task)
+      @tasks << task
+      unless @is_spinning
+        @is_spinning = true
+        JS.global.queueMicrotask -> { @loop_fiber.transfer }
+      end
+    end
+  end
 end
 
 class JS::Object
@@ -30,6 +81,14 @@ def respond_to_missing?(sym, include_private)
     return true if super
     self[sym].typeof == "function"
   end
+
+  def await
+    sched = JS.promise_scheduler
+    unless sched
+      raise "Please start Ruby evaluation with RubyVM.eval_async to use JS::Object#await"
+    end
+    sched.await(self)
+  end
 end
 
 # A wrapper class for JavaScript Error to allow the Error to be thrown in Ruby.

packages/npm-packages/ruby-wasm-wasi/src/index.ts

@@ -225,6 +225,30 @@ export class RubyVM {
     return evalRbCode(this, this.privateObject(), code);
   }
 
+  evalAsync(code: string): Promise<RbValue> {
+    const JS = this.eval("require 'js'; JS");
+    return new Promise((resolve, reject) => {
+      JS.call(
+        "eval_async",
+        this.wrap(code),
+        this.wrap({
+          resolve,
+          reject: (error: RbValue) => {
+            reject(
+              new RbError(
+                this.exceptionFormatter.format(
+                  error,
+                  this,
+                  this.privateObject()
+                )
+              )
+            );
+          },
+        })
+      );
+    });
+  }
+
   /**
    * Wrap a JavaScript value into a Ruby JS::Object
    * @param value The value to convert to RbValue