Do not buffer for simple programs (1 statement)

lib/handlebars/compiler/compiler.js

@@ -127,6 +127,7 @@ Handlebars.JavaScriptCompiler = function() {};
         statement = statements[i];
         this[statement.type](statement);
       }
+      this.isSimple = l === 1;
 
       this.depths.list = this.depths.list.sort(function(a, b) {
         return a - b;
@@ -323,7 +324,11 @@ Handlebars.JavaScriptCompiler = function() {};
     },
 
     appendToBuffer: function(string) {
-      return "buffer += " + string + ";";
+      if (this.environment.isSimple) {
+        return "return " + string + ";";
+      } else {
+        return "buffer += " + string + ";";
+      }
     },
 
     initializeBuffer: function() {
@@ -350,7 +355,7 @@ Handlebars.JavaScriptCompiler = function() {};
 
       this.compileChildren(environment, options);
 
-      var opcodes = environment.opcodes, opcode, name, declareName, declareVal;
+      var opcodes = environment.opcodes, opcode;
 
       this.i = 0;
 
@@ -406,7 +411,11 @@ Handlebars.JavaScriptCompiler = function() {};
         out.push('');
       }
 
-      out.push("var buffer = " + this.initializeBuffer());
+      if (!this.environment.isSimple) {
+        out.push(", buffer = " + this.initializeBuffer());
+      } else {
+        out.push("");
+      }
 
       // track the last context pushed into place to allow skipping the
       // getContext opcode when it would be a noop
@@ -432,14 +441,18 @@ Handlebars.JavaScriptCompiler = function() {};
         }
       }
 
-      this.source[1] = this.source[1] + ";";
+      if (this.source[1]) {
+        this.source[1] = "var " + this.source[1].substring(2) + ";";
+      }
 
       // Merge children
       if (!this.isChild) {
         this.source[1] += '\n' + this.context.programs.join('\n') + '\n';
       }
 
-      this.source.push("return buffer;");
+      if (!this.environment.isSimple) {
+        this.source.push("return buffer;");
+      }
 
       var params = this.isChild ? ["depth0", "data"] : ["Handlebars", "depth0", "helpers", "partials", "data"];
 
@@ -467,6 +480,9 @@ Handlebars.JavaScriptCompiler = function() {};
     append: function() {
       var local = this.popStack();
       this.source.push("if(" + local + " || " + local + " === 0) { " + this.appendToBuffer(local) + " }");
+      if (this.environment.isSimple) {
+        this.source.push("else { " + this.appendToBuffer("''") + " }");
+      }
     },
 
     appendEscaped: function() {