warn when shouldComponentUpdate() returns undefined

Author: danielschonfeld

src/core/ReactCompositeComponent.js

@@ -1000,9 +1000,22 @@ var ReactCompositeComponentMixin = {
  this._pendingState = null;
 
  try {
- if (this._pendingForceUpdate ||
- !this.shouldComponentUpdate ||
- this.shouldComponentUpdate(nextProps, nextState, nextContext)) {
+ var shouldUpdate =
+ this._pendingForceUpdate ||
+ !this.shouldComponentUpdate ||
+ this.shouldComponentUpdate(nextProps, nextState, nextContext);
+
+ if (__DEV__) {
+ if (typeof shouldUpdate === "undefined") {
+ console.warn(
+ (this.constructor.displayName || 'ReactCompositeComponent') +
+ '.shouldComponentUpdate(): Returned undefined instead of a ' +
+ 'boolean value. Make sure to return true or false.'
+ );
+ }
+ }
+
+ if (shouldUpdate) {
  this._pendingForceUpdate = false;
  // Will set `this.props`, `this.state` and `this.context`.
  this._performComponentUpdate(

src/core/__tests__/ReactCompositeComponent-test.js

@@ -871,6 +871,38 @@ describe('ReactCompositeComponent', function() {
  expect(React.isValidClass(TrickFnComponent)).toBe(false);
  });
 
+ it('should warn when shouldComponentUpdate() returns undefined', function() {
+ var warn = console.warn;
+ console.warn = mocks.getMockFunction();
+
+ try {
+ var Component = React.createClass({
+ getInitialState: function () {
+ return {bogus: false};
+ },
+
+ shouldComponentUpdate: function() {
+ return undefined;
+ },
+
+ render: function() {
+ return <div />;
+ }
+ });
+
+ var instance = ReactTestUtils.renderIntoDocument(<Component />);
+ instance.setState({bogus: true});
+
+ expect(console.warn.mock.calls.length).toBe(1);
+ expect(console.warn.mock.calls[0][0]).toBe(
+ 'Component.shouldComponentUpdate(): Returned undefined instead of a ' +
+ 'boolean value. Make sure to return true or false.'
+ );
+ } finally {
+ console.warn = warn;
+ }
+ });
+
  it('should warn when mispelling shouldComponentUpdate', function() {
  var warn = console.warn;
  console.warn = mocks.getMockFunction();