How to access one component's state from another component

How do I access one component's state in another component? Below is my code and I'm trying to access the state of component a in component b.

var a = React.createClass({
    getInitialState: function () {
        return {
            first: "1"
        };
    },

    render: function () {
        // Render HTML here.
    }  
});

var b = React.createClass({
    getInitialState: function () {
        return {
            second: a.state.first
        };
    },

    render: function () {
        // Render HTML here.
    }  
});

But I'm not getting anything.

Solution 1:

Even if you try doing this way, it is not correct method to access the state. Better to have a parent component whose children are a and b. The ParentComponent will maintain the state and pass it as props to the children.

For instance,

var ParentComponent = React.createClass({
  getInitialState : function() {
    return {
      first: 1,
    }
  }

  changeFirst: function(newValue) {
    this.setState({
      first: newValue,
    });
  }

  render: function() {
   return (
     <a first={this.state.first} changeFirst={this.changeFirst.bind(this)} />
     <b first={this.state.first} changeFirst={this.changeFirst.bind(this)} />
   )
 }
}

Now in your child compoenents a and b, access first variable using this.props.first. When you wish to change the value of first call this.props.changeFirst() function of the ParentComponent. This will change the value and will be thus reflected in both the children a and b.

I am writing component a here, b will be similar:

var a = React.createClass({

  render: function() {
    var first = this.props.first; // access first anywhere using this.props.first in child
    // render JSX
  }
}

Solution 2:

If two components need access to the same state they should have a common ancestor where the state is kept.

So component A is the parent of B and C. Component A has the state, and passes it down as props to B and C. If you want to change the state from B you pass down a callback function as a prop.