index.js

/**
 * Copyright (c) 2013-present, Facebook, Inc.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 */

function componentWillMount() {
  // Call this.constructor.gDSFP to support sub-classes.
  var state = this.constructor.getDerivedStateFromProps(this.props, this.state);
  if (state !== null && state !== undefined) {
    this.setState(state);
  }
}

function componentWillReceiveProps(nextProps) {
  // Call this.constructor.gDSFP to support sub-classes.
  // Use the setState() updater to ensure state isn't stale in certain edge cases.
  function updater(prevState) {
    var state = this.constructor.getDerivedStateFromProps(nextProps, prevState);
    return state !== null && state !== undefined ? state : null;
  }
  // Binding "this" is important for shallow renderer support.
  this.setState(updater.bind(this));
}

function componentWillUpdate(nextProps, nextState) {
  try {
    var prevProps = this.props;
    var prevState = this.state;
    this.props = nextProps;
    this.state = nextState;
    this.__reactInternalSnapshotFlag = true;
    this.__reactInternalSnapshot = this.getSnapshotBeforeUpdate(
      prevProps,
      prevState
    );
  } finally {
    this.props = prevProps;
    this.state = prevState;
  }
}

// React may warn about cWM/cWRP/cWU methods being deprecated.
// Add a flag to suppress these warnings for this special case.
componentWillMount.__suppressDeprecationWarning = true;
componentWillReceiveProps.__suppressDeprecationWarning = true;
componentWillUpdate.__suppressDeprecationWarning = true;

export function polyfill(Component) {
  var prototype = Component.prototype;

  if (!prototype || !prototype.isReactComponent) {
    throw new Error('Can only polyfill class components');
  }

  if (
    typeof Component.getDerivedStateFromProps !== 'function' &&
    typeof prototype.getSnapshotBeforeUpdate !== 'function'
  ) {
    return Component;
  }

  // If new component APIs are defined, "unsafe" lifecycles won't be called.
  // Error if any of these lifecycles are present,
  // Because they would work differently between older and newer (16.3+) versions of React.
  var foundWillMountName = null;
  var foundWillReceivePropsName = null;
  var foundWillUpdateName = null;
  if (typeof prototype.componentWillMount === 'function') {
    foundWillMountName = 'componentWillMount';
  } else if (typeof prototype.UNSAFE_componentWillMount === 'function') {
    foundWillMountName = 'UNSAFE_componentWillMount';
  }
  if (typeof prototype.componentWillReceiveProps === 'function') {
    foundWillReceivePropsName = 'componentWillReceiveProps';
  } else if (typeof prototype.UNSAFE_componentWillReceiveProps === 'function') {
    foundWillReceivePropsName = 'UNSAFE_componentWillReceiveProps';
  }
  if (typeof prototype.componentWillUpdate === 'function') {
    foundWillUpdateName = 'componentWillUpdate';
  } else if (typeof prototype.UNSAFE_componentWillUpdate === 'function') {
    foundWillUpdateName = 'UNSAFE_componentWillUpdate';
  }
  if (
    foundWillMountName !== null ||
    foundWillReceivePropsName !== null ||
    foundWillUpdateName !== null
  ) {
    var componentName = Component.displayName || Component.name;
    var newApiName =
      typeof Component.getDerivedStateFromProps === 'function'
        ? 'getDerivedStateFromProps()'
        : 'getSnapshotBeforeUpdate()';

    throw Error(
      'Unsafe legacy lifecycles will not be called for components using new component APIs.\n\n' +
        componentName +
        ' uses ' +
        newApiName +
        ' but also contains the following legacy lifecycles:' +
        (foundWillMountName !== null ? '\n  ' + foundWillMountName : '') +
        (foundWillReceivePropsName !== null
          ? '\n  ' + foundWillReceivePropsName
          : '') +
        (foundWillUpdateName !== null ? '\n  ' + foundWillUpdateName : '') +
        '\n\nThe above lifecycles should be removed. Learn more about this warning here:\n' +
        'https://fb.me/react-async-component-lifecycle-hooks'
    );
  }

  // React <= 16.2 does not support static getDerivedStateFromProps.
  // As a workaround, use cWM and cWRP to invoke the new static lifecycle.
  // Newer versions of React will ignore these lifecycles if gDSFP exists.
  if (typeof Component.getDerivedStateFromProps === 'function') {
    prototype.componentWillMount = componentWillMount;
    prototype.componentWillReceiveProps = componentWillReceiveProps;
  }

  // React <= 16.2 does not support getSnapshotBeforeUpdate.
  // As a workaround, use cWU to invoke the new lifecycle.
  // Newer versions of React will ignore that lifecycle if gSBU exists.
  if (typeof prototype.getSnapshotBeforeUpdate === 'function') {
    if (typeof prototype.componentDidUpdate !== 'function') {
      throw new Error(
        'Cannot polyfill getSnapshotBeforeUpdate() for components that do not define componentDidUpdate() on the prototype'
      );
    }

    prototype.componentWillUpdate = componentWillUpdate;

    var componentDidUpdate = prototype.componentDidUpdate;

    prototype.componentDidUpdate = function componentDidUpdatePolyfill(
      prevProps,
      prevState,
      maybeSnapshot
    ) {
      // 16.3+ will not execute our will-update method;
      // It will pass a snapshot value to did-update though.
      // Older versions will require our polyfilled will-update value.
      // We need to handle both cases, but can't just check for the presence of "maybeSnapshot",
      // Because for <= 15.x versions this might be a "prevContext" object.
      // We also can't just check "__reactInternalSnapshot",
      // Because get-snapshot might return a falsy value.
      // So check for the explicit __reactInternalSnapshotFlag flag to determine behavior.
      var snapshot = this.__reactInternalSnapshotFlag
        ? this.__reactInternalSnapshot
        : maybeSnapshot;

      componentDidUpdate.call(this, prevProps, prevState, snapshot);
    };
  }

  return Component;
}