[javascript] How to access component methods from “outside” in ReactJS?

Why can’t I access the component methods from “outside” in ReactJS? Why is it not possible and is there any way to solve it?

Consider the code:

var Parent = React.createClass({
    render: function() {
        var child = <Child />;
        return (
            <div>
                {child.someMethod()} // expect "bar", got a "not a function" error.
            </div>
        );
    }
});

var Child = React.createClass({
    render: function() {
        return (
            <div>
                foo
            </div>
        );
    },
    someMethod: function() {
        return 'bar';
    }
});

React.renderComponent(<Parent />, document.body);

As mentioned in some of the comments, ReactDOM.render no longer returns the component instance. You can pass a ref callback in when rendering the root of the component to get the instance, like so:

// React code (jsx)
function MyWidget(el, refCb) {
    ReactDOM.render(<MyComponent ref={refCb} />, el);
}
export default MyWidget;

and:

// vanilla javascript code
var global_widget_instance;

MyApp.MyWidget(document.getElementById('my_container'), function(widget) {
    global_widget_instance = widget;
});

global_widget_instance.myCoolMethod();

As of React 16.3 React.createRef can be used, (use ref.current to access)

var ref = React.createRef()

var parent = (
  <div>
    <Child ref={ref} />
    <button onClick={e=>console.log(ref.current)}
  </div>
);

React.renderComponent(parent, document.body)

Alternatively, if the method on Child is truly static (not a product of current props, state) you can define it on statics and then access it as you would a static class method. For example:

var Child = React.createClass({
  statics: {
    someMethod: function() {
      return 'bar';
    }
  },
  // ...
});

console.log(Child.someMethod()) // bar

Since React 0.12 the API is slightly changed. The valid code to initialize myChild would be the following:

var Child = React.createClass({…});
var myChild = React.render(React.createElement(Child, {}), mountNode);
myChild.someMethod();

Another way so easy:

function outside:

function funx(functionEvents, params) {
  console.log("events of funx function: ", functionEvents);
  console.log("this of component: ", this);
  console.log("params: ", params);
  thisFunction.persist();
}

Bind it:

constructor(props) {
   super(props);
    this.state = {};
    this.funxBinded = funx.bind(this);
  }
}

Please see complete tutorial here: How to use "this" of a React Component from outside?

You could also do it like this, not sure if it's a good plan :D

class Parent extends Component {
  handleClick() {
    if (this._getAlert !== null) {
      this._getAlert()
    }
  }

  render() {
    return (
      <div>
        <Child>
        {(getAlert, childScope) => (
          <span> {!this._getAlert ? this._getAlert = getAlert.bind(childScope) : null}</span>
        )}
        </Child>
        <button onClick={() => this.handleClick()}> Click me</button>
      </div>
      );
    }
  }

class Child extends Component {
  constructor() {
    super();
    this.state = { count: 0 }
  }

  getAlert() {
    alert(`Child function called state: ${this.state.count}`);
    this.setState({ count: this.state.count + 1 });
  }

  render() {
    return this.props.children(this.getAlert, this)
  }
}

If you want to call functions on components from outside React, you can call them on the return value of renderComponent:

var Child = React.createClass({…});
var myChild = React.renderComponent(Child);
myChild.someMethod();

The only way to get a handle to a React Component instance outside of React is by storing the return value of React.renderComponent. Source.