message: Replace magical numbers with a constant
  Follow-up to:
diff: @@ -34,6 +34,8 @@ import {
  introspectionQuerySansSubscriptions,
  } from '../utility/introspectionQueries';
  +const DEFAULT_DOC_EXPLORER_WIDTH = 350;
  +
  /**
  * The top-level React component for GraphiQL, intended to encompass the entire
  * browser viewport.
  @@ -111,7 +113,9 @@ export class GraphiQL extends React.Component {
  Number(this._storage.get('variableEditorHeight')) || 200,
  docExplorerOpen: this._storage.get('docExplorerOpen') === 'true' || false,
  historyPaneOpen: this._storage.get('historyPaneOpen') === 'true' || false,
  - docExplorerWidth: Number(this._storage.get('docExplorerWidth')) || 350,
  + docExplorerWidth:
  + Number(this._storage.get('docExplorerWidth')) ||
  + DEFAULT_DOC_EXPLORER_WIDTH,
  isWaitingForResponse: false,
  subscription: null,
  ...queryFacts,
  @@ -890,7 +894,7 @@ export class GraphiQL extends React.Component {
  handleDocsResetResize = () => {
  this.setState({
  - docExplorerWidth: 350,
  + docExplorerWidth: DEFAULT_DOC_EXPLORER_WIDTH,
  });
  };
  