ReactJs - Uncaught TypeError: Cannot read property 'string' of undefined -

my 2 files:

app:

import react, { component } 'react'; import { nice, super_nice } './colors'; import counter './counter';  export class app extends component {   render() {     return (       <div>         <counter increment={ 1 } color={ nice } />         <counter increment={ 5 } color={ super_nice } />       </div>     );   } } 

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counter:

import react, { component } 'react';  class counter extends component {   constructor(props) {     super(props);     this.state = { counter: 0 };     this.interval = setinterval(() => this.tick(), 1000);   }    tick() {     this.setstate({       counter: this.state.counter + this.props.increment     });   }    componentwillunmount() {     clearinterval(this.interval);   }    render() {     return (       <h1 style={ { color: this.props.color } }>         counter ( { this.props.increment } ): { this.state.counter }       </h1>     );   } }  counter.defaultprops = {   increment: 0,   color: null };  counter.proptypes = {   increment: react.proptypes.number.isrequired,   color: react.proptypes.string.isrequired };   module.exports = counter; 

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i using:

"react": "^0.14.0-rc1", "eslint": "^1.3.1", "eslint-config-airbnb": "^0.1.0", "eslint-loader": "^1.0.0", "eslint-plugin-react": "^3.0.0" 

i need declare proptypes satisfy eslint, receiving run-error:

"uncaught typeerror: cannot read property 'string' of undefined".

does see error?

many !

on counter proptypes, "color" react.proptypes should capitalized.

counter.proptypes = {   increment: react.proptypes.number.isrequired,   color: react.proptypes.string.isrequired };