Tom Joad Tom Joad - 4 months ago 68
Javascript Question

How to wait for AJAX response and only after that render the component?

I have a problem with one of my React components. I think AJAX doesn't load all the content from external server before React renders the

ChildComp
component.

Obj tree

Above you can see the tree of response which is coming from server. And this is my component's code:

var ChildComp = React.createClass({
getInitialState: function(){
return {
response: [{}]
}
},
componentWillReceiveProps: function(nextProps){
var self = this;

$.ajax({
type: 'GET',
url: '/subscription',
data: {
subscriptionId: nextProps.subscriptionId //1
},
success: function(data){
self.setState({
response: data
});
console.log(data);
}
});
},
render: function(){
var listSubscriptions = this.state.response.map(function(index){
return (
index.id
)
});
return (
<div>
{listSubscriptions}
</div>
)
}
});


This is working just fine, but if I change my return to:

return (
index.id + " " + index.order.id
)


id is undefined. And all of the other properties of order object. Why is it like this? If I
console.log
my response after
success
function it gives all the data (like in picture). My guess is that only the first objects are loaded when React renders the component and after that all other inner objects are loaded. I can't really say if that's the case (sounds so weird) nor I can't say how to solve this out.

I tried also something like this

success: function(data){
self.setState({
response: data
}, function(){
self.forceUpdate();
})
}.bind(this)


but still re-render happens before my
console.log(data)
is triggered. How to wait for AJAX response and only after that render the component?

Answer

Here's your code reworked with some comments of the modified parts

  getInitialState: function(){
    return {
      // [{}] is weird, either use undefined (or [] but undefined is better).
      // If you use [], you loose the information of a "pending" request, as 
      // you won't be able to make a distinction between a pending request, 
      // and a response that returns an empty array
      response: undefined
    }
  },

  loadSubscriptionData: function(subscriptionId){
    var self = this;

    // You probably want to redo the ajax request only when the 
    // subscriptionId has changed (I guess?)
    var subscriptionIdHasChanged = 
       (this.props.subscriptionId !== subscriptionId)

    if ( subscriptionIdHasChanged ) {
        // Not required, but can be useful if you want to provide the user
        // immediate feedback and erase the existing content before 
        // the new response has been loaded
        this.setState({response: undefined});

        $.ajax({
          type: 'GET',
          url: '/subscription',
          data: {
            subscriptionId: subscriptionId //1
          },
          success: function(data){

            // Prevent concurrency issues if subscriptionId changes often: 
            // you are only interested in the results of the last ajax    
            // request that was made.
            if ( self.props.subscriptionId === subscriptionId ) {
                self.setState({
                  response: data
                });
            }
          }
        });
     }
  },

  // You want to load subscriptions not only when the component update but also when it gets mounted. 
  componentDidMount: function(){
    this.loadSubscriptionData(this.props.subscriptionId);
  },
  componentWillReceiveProps: function(nextProps){
    this.loadSubscriptionData(nextProps.subscriptionId);
  },

  render: function(){

      // Handle case where the response is not here yet
      if ( !this.state.response ) {
         // Note that you can return false it you want nothing to be put in the dom
         // This is also your chance to render a spinner or something...
         return <div>The responsive it not here yet!</div>
      }

      // Gives you the opportunity to handle the case where the ajax request
      // completed but the result array is empty
      if ( this.state.response.length === 0 ) {
          return <div>No result found for this subscription</div>;
      } 


      // Normal case         
      var listSubscriptions = this.state.response.map(function(index){
        return (
          index.id
        )
      });
      return (
        <div>
          {listSubscriptions}
        </div>
      ) 
  }