perf($interpolate): provide a simplified result for constant expressions

Author: jbedard

benchmarks/largetable-bp/main.html

@@ -19,6 +19,7 @@
       <div>interpolation + fnInvocation: <input type="radio" ng-model="benchmarkType" value="interpolationFn"></div>
       <div>ngBind + filter: <input type="radio" ng-model="benchmarkType" value="ngBindFilter"></div>
       <div>interpolation + filter: <input type="radio" ng-model="benchmarkType" value="interpolationFilter"></div>
+      <div>ngModel: <input type="radio" ng-model="benchmarkType" value="ngModel"></div>
 
       <ng-switch on="benchmarkType">
         <baseline-binding-table ng-switch-when="baselineBinding">
@@ -77,6 +78,13 @@ <h2>interpolation with filter</h2>
             <span ng-repeat="column in row">{{column.i | noop}}:{{column.j | noop}}|</span>
           </div>
         </div>
+        <div ng-switch-when="ngModel">
+          <h2>ngModels</h2>
+          <div ng-repeat="row in data">
+            <input type="text" ng-model="row.i" name="constName" />
+            <input type="text" ng-model="row.j" />
+          </div>
+        </div>
       </ng-switch>
     </div>
   </div>

src/ng/interpolate.js

@@ -183,6 +183,18 @@ function $InterpolateProvider() {
      * - `context`: evaluation context for all expressions embedded in the interpolated text
      */
     function $interpolate(text, mustHaveExpression, trustedContext, allOrNothing) {
+      // Provide a quick exit and simplified result function for text with no interpolation
+      if (!text.length || text.indexOf(startSymbol) === -1) {
+        var constantInterp;
+        if (!mustHaveExpression) {
+          constantInterp = function constantInterpolationFn() { return text; };
+          constantInterp.exp = text;
+          constantInterp.constant = true;
+          constantInterp.expressions = [];
+        }
+        return constantInterp;
+      }
+
       allOrNothing = !!allOrNothing;
       var startIndex,
           endIndex,

test/ng/interpolateSpec.js

@@ -8,6 +8,7 @@ describe('$interpolate', function() {
 
     expect(interpolateFn.exp).toBe('some text');
     expect(interpolateFn.expressions).toEqual([]);
+    expect(interpolateFn.constant).toEqual(true);
 
     expect(interpolateFn({})).toBe('some text');
   }));