Add benchmarks

benchmarks/list_ops.js

@@ -0,0 +1,9 @@
+const numbers = [];
+for (let i = 0; i < 30000; i++) {
+  numbers.push(i);
+}
+let s = 0;
+for (let i = 0; i < 30000; i++) {
+  s += numbers[i];
+}
+console.log(s);