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@jondlm /README.md
Last active Jan 15, 2017

React shallow render lifecycle breakdown

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
/*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;
/*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();
@sodiumjoe

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

@smith-kyle

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

@collinjackson93

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.

@QuantumInformation

Nice thanks.

@samidarko

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

@ronny
ronny commented Nov 27, 2015

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

@ngduc
ngduc commented Dec 15, 2015

+1 : how to test componentDidMount? Thanks.

@nali
nali commented Dec 31, 2015

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.

@alopes
alopes commented Jan 11, 2016

+1 componentDidMount

@gwing33
gwing33 commented Jan 15, 2016

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.

@srph
srph commented Jan 15, 2016

@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.

@wwalser
wwalser commented Jun 27, 2016 edited

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.

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