React shallow render lifecycle breakdown

README.md

React introduced shallow rendering in 0.13. This is an excellent feature that I wish was included earlier in React. It aims to solve the problem of unit testing components without going through a real, or jsdom mocked, DOM. I couldn't find any info online about what lifecycle events it actually fires. So I did some testing of my own. To reproduce, put component.js and test.js into a folder and run node test.js.

TLDR; shallow rendering only invokes the following lifecycle hooks (in order):

1. getDefaultProps
2. getInitialState
3. componentWillMount stops here until re-render
4. componentWillReceiveProps
5. shouldComponentUpdate
6. componentWillUpdate

component.js

/*eslint node:1 */
'use strict';

var React = require('react');

var Component = React.createClass({
  getDefaultProps: function () { console.log('getDefaultProps fired'); return { another: true }; },
  getInitialState: function () { console.log('getInitialState fired'); return {}; },

  // Life cycle methods
  componentWillMount: function () { console.log('componentWillMount fired'); },
  componentDidMount: function () { console.log('componentDidMount fired'); },
  componentWillReceiveProps: function () { console.log('componentWillReceiveProps fired'); },
  shouldComponentUpdate: function () { console.log('shouldComponentUpdate fired'); return true; },
  componentWillUpdate: function () { console.log('componentWillUpdate fired'); },
  componentDidUpdate: function () { console.log('componentDidUpdate fired'); },
  componentWillUnmount: function () { console.log('componentWillUnmount fired'); },

  render: function() {
    return React.createElement('div');
  }
});

module.exports = Component;

test.js

/*eslint node:1 */
'use strict';

var React = require('react/addons');
var TestUtils = React.addons.TestUtils;
var Component = require('./component');
var shallowRenderer = TestUtils.createRenderer();

var props = { something: true };

// Trigger first render
shallowRenderer.render(React.createElement(Component, props));
shallowRenderer.getRenderOutput();

// Update props
props.something = false;

// Trigger a re-render
shallowRenderer.render(React.createElement(Component, props));
shallowRenderer.getRenderOutput();

Have you tried this with writing tests? How is it?

Thanks for putting this together! This is really something that should be added to the Shallow Rendering portion of the docs.

Why wouldn't they have it fire all the lifecycle methods? Regardless, thank you for experimenting with this, it certainly saved me a lot of frustration debugging. Maybe one day the official documentation will improve.

Nice thanks.

That's a tricky one. Thanks for the post, so how do we do to test things happening in componentDidMount? Using renderIntoDocument I suppose...

componentWillUnmount will be invoked too after shallowRenderer.unmount() is called.

+1 : how to test componentDidMount? Thanks.

Thanks so much for this. I'm also trying to test componentDidMount without a deep render and was mystified as to why it doesn't get called.

+1 componentDidMount

There use to be a method that grabbed the instance, but in 0.14.6 tag, it doesn't have that method. but if you want to hack it, you can do...

let instance = shallowRenderer._instance._instance;
instance.componentDidMount();

I'd probably avoid shallowRender for this. renderIntoDocument is probably better suited.

@gwing33 - I'm not sure if I understand the context; but the behavior of child components can get in the way if you use renderIntoDocument.

Following up on @gwing33's comment, I believe getMountedInstance() is the name of the method in question. It exists on all >0.15 branches and master. All lifecycle methods should be available through that for manual triggering.