React componentDidMount vs getInitialState

Question

I have some questions about react usage and patterns.

Should I use

componentDidMount

or

getInitialState

in loading data asynchronously? What is the difference between the two?

I am using Backbone for my frontend data structures

this.props.data = new BrandModel({ _id: this.props.params.brandId });
var that = this;
this.props.data.fetch({
  success: function () {
    that.setState({ brand: that.props.brand });
  }
});
return null;

Update: thanks for the responses

This Question is suggesting to not us componentWillMount, but I understand that its more expressive to use componentDidMount in this case as getInitialState seems to be meant to be used synchronously

Update 2:

I've had to revert to using getInitialState as componentDidMount fires after render and I need this.props.data to be pointing to an object

Solution 1

componentDidMount would be called after component was mounted into browser DOM (it would be called after first render and it would not be called if you are rendering server-side(to string)

getInitialState would be called when component is created, if you are using es6 class syntax you can place that logic in you component constructor directly assigning to this.state

There is also componentWillMount it would be called before first render for both server and client - it is more suitable in your case.

Solution 2

Componentndid mount is fired after the render and we load the Ajax inside that.While during the actual render we check if the object has data, else send empty div

componentDidMount: function () {
            console.log("========> FIring");
            $.get("http://api.", function(response) {
                if (this.isMounted()) {
                    this.setState({
                    Data: response
                });
                }
            }.bind(this));
        },
        render: function() {
            var data = this.state.Data;
            if (this.state.promoData) {
             return (<div>{data}</div>
            );
            } else {
              return (<div className="divLoading">Loading...</div>);
            }
        }

Solution 3

I'm not sure about this Backbone usage but if you load data in componentDidMount that's fine as essentially that code will start executing after the component is initially rendered -- after the data is fetched and the state is set again, the component will re-render showing that correct data at that point. This kind of like lazy loading to me.

I'm not sure if getInitialState is blocking, but if it is, then the component will not render until the state is loaded. But I think it isn't, so the data would probably not be fetched by the time the component is rendered.

componentWillMount may be what you want, but review the React lifecycle for what you think makes the most sense.

Comments

[KajMagnus]

getInitialState is not blocking — no React function is, unless one does something like while (true) { console.log('a-long-loop'); }