javascript - ReactJS Uncaught TypeError: Cannot read property '' of null when one method is applied in another -


i use in method visibilityfilter(event){...} method helperfunction(){...}. when push button fire event error: 

uncaught typeerror: cannot read property 'helperfunction' of null

how can rid of error in following code: 

class buttons extends react.component {      helperfunction(){         let number = 2;         return number     };      visibilityfilter(event){          console.info(' helperfunction():',this.helperfunction()); //error here          let action = {type: 'set_visibility_filter',payload: {name: event.target.dataset.filtername, on: true}};         store.dispatch(action);     };     render(){                    return(             <div classname="container-fluid">                 <div classname="row">                     <div classname="col-lg-4 col-md-4 col-sm-4 col-xs-0">                         <buttom type="button" classname="m-t-1-em w-100 btn btn-info" onclick={this.visibilityfilter} data-filter-name="favorite">favorite</buttom>                     </div>                 </div>                           </div>         );     }; }; if(document.queryselector("#test1")){     reactdom.render(         <buttons />,         document.queryselector("#test1")     ); };

with of dimitar christoff: solution problem lies in issue of binding. need add .bind(this) in following piece of code in constructor(props){...}:

this.visibilityfilter.bind(this);

the full code be:

class buttons extends react.component {      constructor(props){         super(props);         this.visibilityfilter.bind(this);     };      helperfunction(){         let number = 2;         return number     };      visibilityfilter(event){         console.info(' helperfunction():',this.helperfunction());         let action = {type: 'set_visibility_filter',payload: {name: event.target.dataset.filtername, on: true}};         store.dispatch(action);     };     render(){                    return(             <div classname="container-fluid">                 <div classname="row">                     <div classname="col-lg-4 col-md-4 col-sm-4 col-xs-0">                         <buttom type="button" classname="m-t-1-em w-100 btn btn-info" onclick={this.visibilityfilter} data-filter-name="favorite">favorite</buttom>                     </div>                 </div>                           </div>         );     }; }; if(document.queryselector("#test1")){     reactdom.render(         <buttons />,         document.queryselector("#test1")     ); };

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