feat: support this expression

src/evaluate.ts

@@ -274,6 +274,10 @@ const evaluate_map = {
       "++": v => ($var.$set(v + 1), prefix ? ++v : v++)
     }[node.operator](evaluate(node.argument, scope));
   },
+  ThisExpression: (node: types.ThisExpression, scope: Scope) => {
+    const this_val = scope.$find("this");
+    return this_val ? this_val.$get() : null;
+  },
   ObjectExpression(node: types.ObjectExpression, scope: Scope) {
     const object = {};
     for (const property of node.properties) {

test/ThisExpression.test.ts

@@ -0,0 +1,26 @@
+import test from "ava";
+import * as fs from "fs";
+
+import vm from "../src/vm";
+
+test("ThisExpression", t => {
+  const sandbox: any = vm.createContext({});
+
+  const func: any = vm.runInContext(
+    `
+function t(){
+  this.name = "hello";
+  return this;
+}
+
+module.exports = t;
+  `,
+    sandbox
+  );
+
+  const ctx: any = {};
+
+  func.call(ctx);
+
+  t.true(ctx.name, "hello");
+});