Evaluate and rimraf... take two!

docs/api.md

@@ -276,10 +276,10 @@ await chromeless.viewport(1024, 800)
 
 ### evaluate<U extends any>(fn: (...args: any[]) => void, ...args: any[]): Chromeless<U>
 
-Evaluate Javascript code within Chrome in the context of the DOM.
+Evaluate Javascript code within Chrome in the context of the DOM. Returns the resulting value or a Promise.
 
 __Arguments__
-- `fn` - Function to evaluate within Chrome
+- `fn` - Function to evaluate within Chrome, can be async (Promise).
 - `[arguments]` - Arguments to pass to the function
 
 __Example__

package.json

@@ -19,8 +19,8 @@
   },
   "scripts": {
     "watch": "tsc -w",
-    "build": "rm -rf dist; tsc -d",
-    "prepublish": "npm run build; npm test",
+    "build": "rimraf dist; tsc -d",
+    "prepublishOnly": "npm test; npm run build",
     "test": "npm run tslint",
     "tslint": "tslint -c tslint.json -p tsconfig.json"
   },

src/util.ts

@@ -134,12 +134,36 @@ export async function evaluate<T>(client: Client, fn: string, ...args: any[]): P
   const {Runtime} = client
   const jsonArgs = JSON.stringify(args)
   const argStr = jsonArgs.substr(1, jsonArgs.length - 2)
-  const expression = `(${fn})(${argStr})`
+
+  const expression = `
+    (() => {
+      const expressionResult = (${fn})(${argStr});
+      if (expressionResult && expressionResult.then) {
+        expressionResult.catch((error) => { throw new Error(error); });
+        return expressionResult;
+      }
+      return Promise.resolve(expressionResult);
+    })();
+  `
 
   const result = await Runtime.evaluate({
     expression,
+    returnByValue: true,
+    awaitPromise: true,
   })
-  return result.result.value
+
+  if (result && result.exceptionDetails) {
+    throw new Error(
+      result.exceptionDetails.exception.value ||
+      result.exceptionDetails.exception.description
+    )
+  }
+
+  if (result && result.result) {
+    return result.result.value
+  }
+
+  return null
 }
 
 export async function type(client: Client, text: string, selector?: string): Promise<void> {