Getting Cannot call a class as a function in my React Project

Question

I m trying to add a React map component to my project but run into an error  I m using Fullstack React s blog post as a reference  I tracked down where the error gets thrown in google map js line 83   function  classCallCheck instance  Constructor       if    instance instanceof Constructor          throw new TypeError  Cannot call a class as a function                  Here is my map component so far  The page loads just fine  without a map  when I comment out lines 58-60  the last three lines  edit  I made the changes that  Dmitriy Nevzorov suggested and it still gives me the same error   import React from  react  import GoogleApiComponent from  google-map-react   export class LocationsContainer extends React Component       constructor             super           render         const style             width   100vw           height   100vh            return          lt div style  style  gt           lt Map google  this props google    gt         lt  div gt               export class Map extends React Component       componentDidUpdate prevProps  prevState           if  prevProps google     this props google               this loadMap                        componentDidMount            this loadMap              loadMap            if  this props  amp  amp  this props google               const  google    this props              const maps   google maps               const mapRef   this refs map              const node   ReactDOM findDOMNode mapRef                let zoom   14              let lat   37 774929             let lng   122 419416             const center   new maps LatLng lat  lng               const mapConfig   Object assign                       center  center                  zoom  zoom                            this map   new maps Map node  mapConfig                      render             return                lt div ref  map  gt                  Loading map                 lt  div gt                     export default GoogleApiComponent     apiKey  MY API KEY    LocationsContainer    And here is where this map component gets routed in main js   import  render  from  react-dom   import React from  react   import Artists from    components Artists  import   Router  Route  Link  browserHistory   from  react-router  import Home from    components HomePage  import Gallery from    components ArtGallery  import ArtistPage from    components ArtistPage  import FavsPage from    components FavsPage  import LocationsContainer from    components Locations     Create the route configuration render      lt Router history  browserHistory  gt       lt Route path     component  Home    gt           lt Route path  locations  component  LocationsContainer    gt           lt Route path  artists  component  Artists    gt            lt Route path  gallery  component  Gallery    gt              lt Route path  favorites  component  FavsPage    gt         lt Route path   artistName  component  ArtistPage    gt     lt  Router gt     document getElementById  app

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For me  it was ComponentName prototype instead of ComponentName propTypes  auto suggested by Phpstorm IDE  Hope it will help someone

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This occured when I accidentally named my render function incorrectly   import React from  react    export class MyComponent extends React Component     noCalledRender         return          lt div gt          Hello  world         lt  div gt                 My instance of this error was simply caused because my class did not have a proper render method

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I faced this error when I imported the wrong class and referred to wrong store while using mobx in react-native   I faced error in this snippet    import   inject  Observer   from  mobx-react     inject   counter    Observer   After few corrections like as below snippet  I resolved my issue like this way   import   inject  observer   from  mobx-react     inject  counterStore    observer   What was actually wrong I was using the wrong class instead of observer I used Observer and instead of counterStore I used counter   I solved my issue like this way

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I experienced the same issue  it occurred because my ES6 component class was not extending React Component

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For me it happened because I didn t wrap my connect function properly  and tried to export default two components

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For me  it was because I d accidentally deleted my render method    I had a class with a componentWillReceiveProps method I didn t need anymore  immediately preceding a short render method   In my haste removing it  I accidentally removed the entire render method as well   This was a PAIN to track down  as I was getting console errors pointing at comments in completely irrelevant files as being the  source  of the problem

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If you re on Node JS and you re seeing this error in a Class you ve added to support a Cucumber test  it s because Cucumber will automatically try to run anything that exports a function  and NodeJS internally converts a Class to a function   So instead of this   module exports   MyClass    do this   module exports MyClass   MyClass    Then  when you import it into your steps file  do it like this   let MyClass   require  myclass js   MyClass    This way you re not exporting a function   Read more here

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I have also run into this  it is possible you have a javascript error inside of your react component  Make sure if you are using a dependency you are using the new operator on the class to instantiate the new instance  Error will throw if  this classInstance   Class      instead use  this classInstance   new Class      you will see in the error chain in the browser  at ReactCompositeComponentWrapper  constructComponentWithoutOwner  that is the giveaway I believe

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For me it was a wrong import of a reducer in the rootReducer js  I imported container instead of reducer file   Example  import settings from    pages Settings     But sure it should be   import settings from    pages Settings reducer     Where settings directory contains following files actions js  index js  reducer js   To check it you can log reducers arg of the assertReducerShape   function from the redux es redux js

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In my case i wrote comment in place of Component by mistake  I just wrote this   import React    Component   from  react      class Something extends Component        render               return                 Instead of this   import React    Component   from  react      class Something extends comment        render               return                 it s not a big deal but for a beginner like me it s really confusing  I hope this will be helpfull

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I had it when I did so    function foo         export default foo   correctly   export default       gt          or  const foo       export default foo

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I experienced this when writing an import statement wrong while importing a function  rather than a class  If removeMaterial is a function in another module   Right   import   removeMaterial   from    ClaimForm     Wrong   import removeMaterial from    ClaimForm

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Mostly these issues occur when you miss extending Component from react   import React   Component  from  react   export default class TimePicker extends Component       render             return

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I received this error by making small mistake  My error was exporting the class as a function instead of as a class  At the bottom of my class file I had   export default InputField      when it should have been   export default InputField

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In my case  using JSX a parent component  was calling other components without the   lt       lt ComponentA someProp  someCheck   ComponentX   ComponentY    gt    fix    lt ComponentA someProp  someCheck    lt ComponentX   gt     lt ComponentY   gt     gt

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In file MyComponent js  export default class MyComponent extends React Component           I put some function related to that component   export default class MyComponent extends React Component          export myFunction             and then in another file imported that function   import myFunction from    MyComponent      myFunction        gt  bang   Cannot call a class as a function        Can you spot the problem   I forgot the curly braces  and imported MyComponent under name myFunction   So  the fix was   import  myFunction  from    MyComponent

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In my case  I accidentally put component name  Home  as the first argument to connect function while it was supposed to be at the end  duh   This one -surely- gave me the error   export default connect Home  mapStateToProps  mapDispatchToProps    But this one worked -surely- fine   export default connect mapStateToProps  mapDispatchToProps  Home

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Post proptypes          to  Post propTypes          someone should comment on how to monitor such error in a very precise way

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For me it happened when I forgot to write extends React Component at the end  I know it s not exactly what YOU had  but others reading this answer can benefit from this  hopefully

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I had a similar problem I was calling the render method incorrectly  Gave an error   render        gt                instead of  correct    render

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Looks like there re no single case when this error appears   Happened to me when I didn t declare constructor in statefull component   class MyComponent extends Component        render             return  lt div gt Test lt  div gt             instead of  class MyComponent extends Component        constructor props            super props              render             return  lt div gt Test lt  div gt

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Hi in my case solutions here won t work My code    index js  import App from    App    let store   createStore App    render       lt Provider store  store  gt           lt Router history  browserHistory  gt               lt Route path     name  Strona gl  wna  component  App  gt                   lt IndexRoute name    component  Welcome   gt                   lt Route name  Dashboard  path  dashboard  component  ReatEstateList   gt    Error apeares in App js after import   Uncaught TypeError  Cannot call a class as a function

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Actually all the problem redux connect  solutions   Correct    export default connect mapStateToProps  mapDispatchToProps  PageName    Wrong  amp  Bug    export default connect PageName  mapStateToProps  mapDispatchToProps

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Another report here  It didn t work as I exported    export default compose    injectIntl    connect mapStateToProps  Onboarding       instead of   export default compose    injectIntl    connect mapStateToProps    Onboarding     Note the position of the brackets  Both are correct and won t get caught by either a linter or prettier or something similar  Took me a while to track it down

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For me it was because i used prototype instead of propTypes  class MyComponent extends Component     render         return  lt div gt Test lt  div gt          MyComponent prototype           it ought to be   MyComponent propTypes

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For me it was because I forgot to use the new keyword when setting up Animated state   eg   fadeAnim  Animated Value 0    to  fadeAnim  new Animated Value 0    would fix it

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Happened to me because I used  PropTypes arrayOf SomeClass   instead of  PropTypes arrayOf PropTypes instanceOf SomeClass

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Two things you can check is   class Slider extends React Component          Your React Code    Slider propTypes            accessibility  PropTypes bool       Make sure that you extends React Component Use propTypes instead of prototype  as per IDE intellisense

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You have duplicated export default declaration  The first one get overridden by second one which is actually a function

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Try stopping you HMR and hit npm start again to rebuild you project  This  made the error to disappear  don t know why

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This is a general issue  and doesn t appear in a single case  But  the common problem in all the cases is that you forget to import a specific component  doesn t matter if it s either from a library that you installed or a custom made component that you created    import  SomeClass  from  some-library   When you use it later  without importing it  the compiler thinks it s a function  Therefore  it breaks  This is a common example   imports     code     and then somewhere inside your code   lt Image    some props    gt   If you forgot to import the component  lt Image   gt  then the compiler will not complain like it does for other imports  but will break when it reaches your code

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tl dr If you use React Router v4 check your  lt Route  gt  component if you indeed use the component prop to pass your class based React component  More generally  If your class seems ok  check if the code that calls it doesn t try to use it as a function  Explanation I got this error because I was using React Router v4 and I accidentally used the render prop instead of the component one in the  lt Route  gt  component to pass my component that was a class  This was a problem  because render expects  calls  a function  while component is the one that will work on React components  So in this code   lt HashRouter gt       lt Switch gt           lt Route path  quot   quot  render  MyComponent    gt       lt  Switch gt   lt  HashRouter gt   The line containing the  lt Route  gt  component  should have been written like this   lt Route path  quot   quot  component  MyComponent    gt   It is a shame  that they don t check it and give a usable error for such and easy to catch mistake

[javascript] Getting "Cannot call a class as a function" in my React Project

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