• i am trying to debug my react code.
• in my render method I try to put debugger and debugger.
• after I step over retun method its going to warning.js.
• after I step over warning.js if conditions its going to instantiateReactComponent.js
• I am not sure why its going to different files. can you tell me why its going to different files.
• not sure how to debug.
• it would be great if you guys give me some explaination so that in future I can fix the error my self

• providing the snippet of the code where it goes in step over function call each time

  error invariant.js?f23e:39 Uncaught Error: Invariant Violation: Element type is invalid: expected a string (for built-in components) or a class/function (for composite components) but got: undefined. Check the render method of sports-container.

  render() { const { sportsType, sportsDevice, sportsWordings, id } = this.props; let sportsEvent = true;

      debugger;
  
      if (sportsEvent === true) {
          return (
  

  warning.js

/** * Similar to invariant but only logs a warning if the condition is not met. * This can be used to log issues in development environments in critical * paths. Removing the logging code for production environments will keep the * same logic and follow the same code paths. */

var warning = emptyFunction;

if (process.env.NODE_ENV !== 'production') {
  warning = function (condition, format) {
    for (var _len = arguments.length, args = Array(_len > 2 ? _len - 2 : 0), _key = 2; _key < _len; _key++) {
      args[_key - 2] = arguments[_key];
    }

    if (format === undefined) {
      throw new Error('`warning(condition, format, ...args)` requires a warning ' + 'message argument');
    }

    if (format.indexOf('Failed Composite propType: ') === 0) {
      return; // Ignore CompositeComponent proptype check.
    }

    if (!condition) {
      var argIndex = 0;
      var message = 'Warning: ' + format.replace(/%s/g, function () {
        return args[argIndex++];
      });
      if (typeof console !== 'undefined') {
        console.error(message);
      }
      try {
        // --- Welcome to debugging React ---
        // This error was thrown as a convenience so that you can use this stack
        // to find the callsite that caused this warning to fire.
        throw new Error(message);
      } catch (x) {}
    }
  };
}

instantiateReactComponent

  instance.construct(node);

/** * Given a ReactNode, create an instance that will actually be mounted. * * @param {ReactNode} node * @return {object} A new instance of the element's constructor. * @protected */

function instantiateReactComponent(node) {
  var instance;

  if (node === null || node === false) {
    instance = new ReactEmptyComponent(instantiateReactComponent);
  } else if (typeof node === 'object') {
    var element = node;
    !(element && (typeof element.type === 'function' || typeof element.type === 'string')) ? process.env.NODE_ENV !== 'production' ? invariant(false, 'Element type is invalid: expected a string (for built-in components) ' + 'or a class/function (for composite components) but got: %s.%s', element.type == null ? element.type : typeof element.type, getDeclarationErrorAddendum(element._owner)) : invariant(false) : undefined;

    // Special case string values
    if (typeof element.type === 'string') {
      instance = ReactNativeComponent.createInternalComponent(element);
    } else if (isInternalComponentType(element.type)) {
      // This is temporarily available for custom components that are not string
      // representations. I.e. ART. Once those are updated to use the string
      // representation, we can drop this code path.
      instance = new element.type(element);
    } else {
      instance = new ReactCompositeComponentWrapper();
    }
  } else if (typeof node === 'string' || typeof node === 'number') {
    instance = ReactNativeComponent.createInstanceForText(node);
  } else {
    !false ? process.env.NODE_ENV !== 'production' ? invariant(false, 'Encountered invalid React node of type %s', typeof node) : invariant(false) : undefined;
  }

  if (process.env.NODE_ENV !== 'production') {
    process.env.NODE_ENV !== 'production' ? warning(typeof instance.construct === 'function' && typeof instance.mountComponent === 'function' && typeof instance.receiveComponent === 'function' && typeof instance.unmountComponent === 'function', 'Only React Components can be mounted.') : undefined;
  }

  // Sets up the instance. This can probably just move into the constructor now.
  instance.construct(node);

• i am trying to debug my react code.
• in my render method I try to put debugger and debugger.
• after I step over retun method its going to warning.js.
• after I step over warning.js if conditions its going to instantiateReactComponent.js
• I am not sure why its going to different files. can you tell me why its going to different files.
• not sure how to debug.
• it would be great if you guys give me some explaination so that in future I can fix the error my self

• providing the snippet of the code where it goes in step over function call each time

  error invariant.js?f23e:39 Uncaught Error: Invariant Violation: Element type is invalid: expected a string (for built-in components) or a class/function (for composite components) but got: undefined. Check the render method of sports-container.

  render() { const { sportsType, sportsDevice, sportsWordings, id } = this.props; let sportsEvent = true;

      debugger;
  
      if (sportsEvent === true) {
          return (
  

  warning.js

/** * Similar to invariant but only logs a warning if the condition is not met. * This can be used to log issues in development environments in critical * paths. Removing the logging code for production environments will keep the * same logic and follow the same code paths. */

var warning = emptyFunction;

if (process.env.NODE_ENV !== 'production') {
  warning = function (condition, format) {
    for (var _len = arguments.length, args = Array(_len > 2 ? _len - 2 : 0), _key = 2; _key < _len; _key++) {
      args[_key - 2] = arguments[_key];
    }

    if (format === undefined) {
      throw new Error('`warning(condition, format, ...args)` requires a warning ' + 'message argument');
    }

    if (format.indexOf('Failed Composite propType: ') === 0) {
      return; // Ignore CompositeComponent proptype check.
    }

    if (!condition) {
      var argIndex = 0;
      var message = 'Warning: ' + format.replace(/%s/g, function () {
        return args[argIndex++];
      });
      if (typeof console !== 'undefined') {
        console.error(message);
      }
      try {
        // --- Welcome to debugging React ---
        // This error was thrown as a convenience so that you can use this stack
        // to find the callsite that caused this warning to fire.
        throw new Error(message);
      } catch (x) {}
    }
  };
}

instantiateReactComponent

  instance.construct(node);

/** * Given a ReactNode, create an instance that will actually be mounted. * * @param {ReactNode} node * @return {object} A new instance of the element's constructor. * @protected */

function instantiateReactComponent(node) {
  var instance;

  if (node === null || node === false) {
    instance = new ReactEmptyComponent(instantiateReactComponent);
  } else if (typeof node === 'object') {
    var element = node;
    !(element && (typeof element.type === 'function' || typeof element.type === 'string')) ? process.env.NODE_ENV !== 'production' ? invariant(false, 'Element type is invalid: expected a string (for built-in components) ' + 'or a class/function (for composite components) but got: %s.%s', element.type == null ? element.type : typeof element.type, getDeclarationErrorAddendum(element._owner)) : invariant(false) : undefined;

    // Special case string values
    if (typeof element.type === 'string') {
      instance = ReactNativeComponent.createInternalComponent(element);
    } else if (isInternalComponentType(element.type)) {
      // This is temporarily available for custom components that are not string
      // representations. I.e. ART. Once those are updated to use the string
      // representation, we can drop this code path.
      instance = new element.type(element);
    } else {
      instance = new ReactCompositeComponentWrapper();
    }
  } else if (typeof node === 'string' || typeof node === 'number') {
    instance = ReactNativeComponent.createInstanceForText(node);
  } else {
    !false ? process.env.NODE_ENV !== 'production' ? invariant(false, 'Encountered invalid React node of type %s', typeof node) : invariant(false) : undefined;
  }

  if (process.env.NODE_ENV !== 'production') {
    process.env.NODE_ENV !== 'production' ? warning(typeof instance.construct === 'function' && typeof instance.mountComponent === 'function' && typeof instance.receiveComponent === 'function' && typeof instance.unmountComponent === 'function', 'Only React Components can be mounted.') : undefined;
  }

  // Sets up the instance. This can probably just move into the constructor now.
  instance.construct(node);

• javascript
• jquery
• reactjs
• react-native
• redux

• The return value of your render call is cut off in your question. – azium Commented Apr 8, 2016 at 14:15
• @azium can you tell me why its jumping between different files when I do step over function in debuggers – user6015171 Commented Apr 8, 2016 at 14:25
• Because functions are defined in different files? And because functions can get passed around as callbacks, so the callee can also be in a different file. I think your problem is not too difficult to solve, but if you don't show us your entire render function we'll never know. – azium Commented Apr 8, 2016 at 17:34
• @all why did you guys mark it negative...I tried but not able to find the solution :( – user6015171 Commented Apr 8, 2016 at 18:08
• @azium hey but I didn't write warning.js but when I debug its going there do you know why...i understood I posted only half of my render method since I am more interested in developer tools debugging :( – user6015171 Commented Apr 8, 2016 at 18:10

2 Answers 2

Check your import / require statements in your file, as well as the export for the components you're importing/requiring. When I get errors like this, it's usually because I'm either importing it incorrectly (ES6), i.e.

import MyComponent from './my-component'

instead of

import { MyComponent } from './my-component'

or maybe I've exported it incorrectly (forgetting to export default, or maybe exporting as default when I didn't mean to), or I forgot to export the component entirely.

In my Case the problem was with nextjs swcMinify enabled, in case of Most people the problem is with imports, I think eslint-import plugin will help to identify bad imports