Scoping in React + React Router

Question

I am having a scoping issue. I can console.log this.props.routeParams.key from within the constructor. But when outside of the constructor, within the filterList function, I get the error "Uncaught TypeError: Cannot read property 'props' of undefined". What's my scoping issue? Why can it read the this from within the constructor but not from within the filterList function?

I am using React Router + Flux + React.

import AltContainer from 'alt-container';
import React from 'react';
import { Link } from 'react-router';
import Blogger from './Blogger'
import List from './List'
const rootURL = 'https://incandescent-fire-6143.firebaseio.com/';

import BlogStore from '../stores/BlogStore'
import BlogActions from '../actions/BlogActions';


export default class BlogShow extends React.Component {
  constructor(props) {
    super(props);
    {console.log(this.props.routeParams.key)}
}


filterList(key) {
  if (this.props.routeParams.key===key){
    return Blogstore.state.blog
  }
}

  render() {
             {Object.keys(BlogStore.state.blog).map(this.filterList)}
  }
}

Answer 1

that is happening because your filterList function is not bound to your component

Bind it in your constructor

constructor(props) {
    super(props);
    this.filterList = this.filterList.bind(this);
}

You read about it here