warning.js:33 Warning: Cannot update during an existing state transition (such as within `render` or another component's constructor). Render methods should be a pure function of props and state; constructor side-effects are an anti-pattern, but can be moved to `componentWillMount`.
printWarning @ warning.js:33
warning @ warning.js:57
warnAboutInvalidUpdates @ react-dom.development.js:9783
scheduleWorkImpl @ react-dom.development.js:10711
scheduleWork @ react-dom.development.js:10689
enqueueSetState @ react-dom.development.js:6212
Component.setState @ react.development.js:237
changeClass @ side.js:83
render @ side.js:90
finishClassComponent @ react-dom.development.js:7873
updateClassComponent @ react-dom.development.js:7850
beginWork @ react-dom.development.js:8225
performUnitOfWork @ react-dom.development.js:10224
workLoop @ react-dom.development.js:10288
callCallback @ react-dom.development.js:542
invokeGuardedCallbackDev @ react-dom.development.js:581
invokeGuardedCallback @ react-dom.development.js:438
renderRoot @ react-dom.development.js:10366
performWorkOnRoot @ react-dom.development.js:11014
performWork @ react-dom.development.js:10967
requestWork @ react-dom.development.js:10878
scheduleWorkImpl @ react-dom.development.js:10732
scheduleWork @ react-dom.development.js:10689
scheduleTopLevelUpdate @ react-dom.development.js:11193
updateContainer @ react-dom.development.js:11231
(anonymous) @ react-dom.development.js:15226
unbatchedUpdates @ react-dom.development.js:11102
renderSubtreeIntoContainer @ react-dom.development.js:15225
render @ react-dom.development.js:15290
(anonymous) @ index.js:28
(anonymous) @ index.js:33
./src/index.js @ main.js:390
__webpack_require__ @ main.js:20
(anonymous) @ main.js:69
(anonymous) @ main.js:72
invariant.js:42 Uncaught Error: Maximum update depth exceeded. This can happen when a component repeatedly calls setState inside componentWillUpdate or componentDidUpdate. React limits the number of nested updates to prevent infinite loops.
    at invariant (invariant.js:42)
    at requestWork (react-dom.development.js:10833)
    at scheduleWorkImpl (react-dom.development.js:10732)
    at scheduleWork (react-dom.development.js:10689)
    at Object.enqueueSetState (react-dom.development.js:6212)
    at Side.Component.setState (react.development.js:237)
    at Side.changeClass (side.js:83)
    at Side.render (side.js:90)
    at finishClassComponent (react-dom.development.js:7873)
    at updateClassComponent (react-dom.development.js:7850)
invariant @ invariant.js:42
requestWork @ react-dom.development.js:10833
scheduleWorkImpl @ react-dom.development.js:10732
scheduleWork @ react-dom.development.js:10689
enqueueSetState @ react-dom.development.js:6212
Component.setState @ react.development.js:237
changeClass @ side.js:83
render @ side.js:90
finishClassComponent @ react-dom.development.js:7873
updateClassComponent @ react-dom.development.js:7850
beginWork @ react-dom.development.js:8225
performUnitOfWork @ react-dom.development.js:10224
workLoop @ react-dom.development.js:10288
callCallback @ react-dom.development.js:542
invokeGuardedCallbackDev @ react-dom.development.js:581
invokeGuardedCallback @ react-dom.development.js:438
renderRoot @ react-dom.development.js:10366
performWorkOnRoot @ react-dom.development.js:11014
performWork @ react-dom.development.js:10967
requestWork @ react-dom.development.js:10878
scheduleWorkImpl @ react-dom.development.js:10732
scheduleWork @ react-dom.development.js:10689
scheduleTopLevelUpdate @ react-dom.development.js:11193
updateContainer @ react-dom.development.js:11231
(anonymous) @ react-dom.development.js:15226
unbatchedUpdates @ react-dom.development.js:11102
renderSubtreeIntoContainer @ react-dom.development.js:15225
render @ react-dom.development.js:15290
(anonymous) @ index.js:28
(anonymous) @ index.js:33
./src/index.js @ main.js:390
__webpack_require__ @ main.js:20
(anonymous) @ main.js:69
(anonymous) @ main.js:72
react-dom.development.js:9747 The above error occurred in the <Side> component:
    in Side (created by Letter)
    in div (created by Letter)
    in Letter (created by Name)
    in div (created by Name)
    in Name
    in div

Consider adding an error boundary to your tree to customize error handling behavior.
Visit https://fb.me/react-error-boundaries to learn more about error boundaries.
logCapturedError @ react-dom.development.js:9747
captureError @ react-dom.development.js:10540
renderRoot @ react-dom.development.js:10391
performWorkOnRoot @ react-dom.development.js:11014
performWork @ react-dom.development.js:10967
requestWork @ react-dom.development.js:10878
scheduleWorkImpl @ react-dom.development.js:10732
scheduleWork @ react-dom.development.js:10689
scheduleTopLevelUpdate @ react-dom.development.js:11193
updateContainer @ react-dom.development.js:11231
(anonymous) @ react-dom.development.js:15226
unbatchedUpdates @ react-dom.development.js:11102
renderSubtreeIntoContainer @ react-dom.development.js:15225
render @ react-dom.development.js:15290
(anonymous) @ index.js:28
(anonymous) @ index.js:33
./src/index.js @ main.js:390
__webpack_require__ @ main.js:20
(anonymous) @ main.js:69
(anonymous) @ main.js:72
invariant.js:42 Uncaught Error: Maximum update depth exceeded. This can happen when a component repeatedly calls setState inside componentWillUpdate or componentDidUpdate. React limits the number of nested updates to prevent infinite loops.
    at invariant (invariant.js:42)
    at requestWork (react-dom.development.js:10833)
    at scheduleWorkImpl (react-dom.development.js:10732)
    at scheduleErrorRecovery (react-dom.development.js:10748)
    at captureError (react-dom.development.js:10562)
    at renderRoot (react-dom.development.js:10391)
    at performWorkOnRoot (react-dom.development.js:11014)
    at performWork (react-dom.development.js:10967)
    at requestWork (react-dom.development.js:10878)
    at scheduleWorkImpl (react-dom.development.js:10732)