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Warn if class has a render() method but doesn't extend React.Component #11168

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merged 4 commits into from
Oct 31, 2017
Merged

Warn if class has a render() method but doesn't extend React.Component #11168

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59d9c06
Merge pull request #1 from facebook/master
swyxio Oct 28, 2017
854daa9
added forgotExtendClass warning on new master
Oct 29, 2017
e8d3851
Tweak the test to assert in all cases
gaearon Oct 31, 2017
97e3a77
Simplify the condition
gaearon Oct 31, 2017
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26 changes: 26 additions & 0 deletions packages/react-dom/src/__tests__/ReactCompositeComponent-test.js
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Original file line number Diff line number Diff line change
Expand Up @@ -326,6 +326,32 @@ describe('ReactCompositeComponent', () => {
expect(cbCalled).toBe(false);
});

it(
'should throw an Error with a warning when rendering' +
"a class with a render method that doesn't extend React.Component",
() => {
spyOn(console, 'error');
var container = document.createElement('div');
class ClassWithRenderNotExtended {
render() {
return <div />;
}
}
expectDev(console.error.calls.count()).toBe(0);
try {
ReactDOM.render(<ClassWithRenderNotExtended />, container);
} catch (e) {
expect(e).toEqual(new TypeError('Cannot call a class as a function'));
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This only runs assertions if we get into catch. But what if we have a bug that causes us not to throw an error? Then the test doesn't assert anything.

expectDev(console.error.calls.count()).toBe(1);
expectDev(console.error.calls.argsFor(0)[0]).toContain(
'Warning: The <ClassWithRenderNotExtended /> component appears to have a render method, ' +
"but doesn't extend React.Component. This is likely to cause errors. " +
'Change ClassWithRenderNotExtended to extend React.Component instead.',
);
}
},
);

it('should warn about `setState` in render', () => {
spyOn(console, 'error');

Expand Down
12 changes: 12 additions & 0 deletions packages/react-reconciler/src/ReactFiberBeginWork.js
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Original file line number Diff line number Diff line change
Expand Up @@ -39,6 +39,7 @@ var {
} = require('shared/ReactTypeOfSideEffect');
var {ReactCurrentOwner} = require('shared/ReactGlobalSharedState');
var invariant = require('fbjs/lib/invariant');
var getComponentName = require('shared/getComponentName');

var ReactFiberClassComponent = require('./ReactFiberClassComponent');
var {
Expand Down Expand Up @@ -471,6 +472,17 @@ module.exports = function<T, P, I, TI, PI, C, CC, CX, PL>(
var value;

if (__DEV__) {
const classWithRenderButNotExtendedFromReactComponent =
workInProgress.type.prototype && workInProgress.type.prototype.render;
if (classWithRenderButNotExtendedFromReactComponent) {
warning(
false,
"The <%s /> component appears to have a render method, but doesn't extend React.Component. " +
'This is likely to cause errors. Change %s to extend React.Component instead.',
getComponentName(workInProgress),
getComponentName(workInProgress),
);
}
ReactCurrentOwner.current = workInProgress;
value = fn(props, context);
} else {
Expand Down