Acorn: top-level parsing experiment

acorn-top-level.js

// See https://jsperf.com/acorn-top-level-parsing-experiment/1 for example  

acorn.plugins.top_level = function (instance) {
      // Could skip other things as well, but this
      // is where the most time can be saved
      instance.parseBlock = function () {
          var node = this.startNode();
          var length = this.context.length;
          do {
              this.next();
          } while (this.context.length >= length);
          this.next(); // this.expect(tt.braceR);
          node.body = [];
          return this.finishNode(node, "BlockStatement");
      };
  };