why-did-you-update.js

/* eslint-disable no-console */
import _ from 'lodash';

/*
Drop this mixin into a component that wastes time according to Perf.getWastedTime() to find
out what state/props should be preserved. Once it says "Update avoidable!" for {state, props},
you should be able to drop in React.addons.PureRenderMixin

React.createClass {
  mixins: [WhyDidYouUpdateMixin]
}

class MyThing extends Component {
  constructor(props) {
    super(props);
    this.componentDidUpdate = WhyDidYouUpdateMixin.componentDidUpdate.bind(this);
  }
}
*/
function isRequiredUpdateObject(o) {
  return Array.isArray(o) || (o && o.constructor === Object.prototype.constructor);
}

function deepDiff(o1, o2, p) {
  const notify = (status) => {
    console.warn('Update %s', status);
    console.log('%cbefore', 'font-weight: bold', o1);
    console.log('%cafter ', 'font-weight: bold', o2);
  };
  if (!_.isEqual(o1, o2)) {
    console.group(p);
    if ([o1, o2].every(_.isFunction)) {
      notify('avoidable?');
    } else if (![o1, o2].every(isRequiredUpdateObject)) {
      notify('required.');
    } else {
      const keys = _.union(_.keys(o1), _.keys(o2));
      for (const key of keys) {
        deepDiff(o1[key], o2[key], key);
      }
    }
    console.groupEnd();
  } else if (o1 !== o2) {
    console.group(p);
    notify('avoidable!');
    if (_.isObject(o1) && _.isObject(o2)) {
      const keys = _.union(_.keys(o1), _.keys(o2));
      for (const key of keys) {
        deepDiff(o1[key], o2[key], key);
      }
    }
    console.groupEnd();
  }
}

const WhyDidYouUpdateMixin = {
  componentDidUpdate(prevProps, prevState) {
    deepDiff({props: prevProps, state: prevState},
             {props: this.props, state: this.state},
             this.constructor.displayName);
  },
};

export default WhyDidYouUpdateMixin;