react prevent children render ( ajax loader waiting for response ) - ajax

Question

Im trying to write simple ajax loader and I wondering that i can prevent props.children render in parent container. The problem is that children want to render, no matter that Loader want to show it or not, and if render is based on ajax data that cousing errors.
Example: https://jsfiddle.net/j8dvsq39/
Example2:
This example will produce error couse this.state.data.user is undefined before ajax request.
Loader:
import React from 'react'
export default React.createClass({
getDefaultProps() {
return { text: "Loading", loaded: false };
},
render() {
if(this.props.loaded == false)
return <div>{this.props.text}</div>;
else
return <div>{this.props.children}</div>;
}
})
Class using Loader
import React from 'react'
import Loader from '../helpers/Loader';
import {comm} from '../Comm';
export default React.createClass({
getInitialState() {
return {loaded: false, data: null};
},
componentWillMount(){
comm.get("/xxx/xxx", {json: 1}, (back) => {
console.log(back);
this.setState({loaded: true, data: back});
});
},
render(){
return <Loader loaded={this.state.loaded}>{this.state.data.user.name}</Loader>
});

Answer 1

Reason is, initially you defined data=null and before the ajax call you are using this.state.data.user.name, it will throw the error:
Cannot read property 'name' of undefined
Simple solution is you need to put the check on data until you didn't get the ajax response, Check this:
var Loader = React.createClass({
getDefaultProps() {
return { text: "Loading", loaded: false };
},
render() {
if(this.props.loaded == false)
return <div>{this.props.text}</div>;
else
return <div>{this.props.children}</div>;
}
});
var Hello = React.createClass({
getInitialState() {
return {loaded: false, data: null};
},
componentWillMount(){
setTimeout(()=>{
this.setState({loaded: true, data: {user:{name: "login"}}});
}, 1000);
},
render: function() {
var user = null;
return <Loader loaded={this.state.loaded}>
<div>
Hello {this.state.data ? this.state.data.user.name : null}
</div>
</Loader>;
}
});
ReactDOM.render(
<Hello name="World" />,
document.getElementById('container')
);
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react-dom.min.js"></script>
<div id='container'/>