What is the best way to trigger onchange event in react js

For React 16 and React >=15.6

Setter .value= is not working as we wanted because React library overrides input value setter but we can call the function directly on the input as context.

var nativeInputValueSetter = Object.getOwnPropertyDescriptor(window.HTMLInputElement.prototype, "value").set;
nativeInputValueSetter.call(input, 'react 16 value');

var ev2 = new Event('input', { bubbles: true});
input.dispatchEvent(ev2);

For textarea element you should use prototype of HTMLTextAreaElement class.

New codepen example.

All credits to this contributor and his solution

Outdated answer only for React <=15.5

With react-dom ^15.6.0 you can use simulated flag on the event object for the event to pass through

var ev = new Event('input', { bubbles: true});
ev.simulated = true;
element.value = 'Something new';
element.dispatchEvent(ev);

I made a codepen with an example

To understand why new flag is needed I found this comment very helpful:

The input logic in React now dedupe's change events so they don't fire more than once per value. It listens for both browser onChange/onInput events as well as sets on the DOM node value prop (when you update the value via javascript). This has the side effect of meaning that if you update the input's value manually input.value = 'foo' then dispatch a ChangeEvent with { target: input } React will register both the set and the event, see it's value is still `'foo', consider it a duplicate event and swallow it.

This works fine in normal cases because a "real" browser initiated event doesn't trigger sets on the element.value. You can bail out of this logic secretly by tagging the event you trigger with a simulated flag and react will always fire the event. https://github.com/jquense/react/blob/9a93af4411a8e880bbc05392ccf2b195c97502d1/src/renderers/dom/client/eventPlugins/ChangeEventPlugin.js#L128

Expanding on the answer from Grin/Dan Abramov, this works across multiple input types. Tested in React >= 15.5

const inputTypes = [
    window.HTMLInputElement,
    window.HTMLSelectElement,
    window.HTMLTextAreaElement,
];

export const triggerInputChange = (node, value = '') => {

    // only process the change on elements we know have a value setter in their constructor
    if ( inputTypes.indexOf(node.__proto__.constructor) >-1 ) {

        const setValue = Object.getOwnPropertyDescriptor(node.__proto__, 'value').set;
        const event = new Event('input', { bubbles: true });

        setValue.call(node, value);
        node.dispatchEvent(event);

    }

};

I know this answer comes a little late but I recently faced a similar problem. I wanted to trigger an event on a nested component. I had a list with radio and check box type widgets (they were divs that behaved like checkboxes and/or radio buttons) and in some other place in the application, if someone closed a toolbox, I needed to uncheck one.

I found a pretty simple solution, not sure if this is best practice but it works.

var event = new MouseEvent('click', {
 'view': window, 
 'bubbles': true, 
 'cancelable': false
});
var node = document.getElementById('nodeMyComponentsEventIsConnectedTo');
node.dispatchEvent(event);

This triggered the click event on the domNode and my handler attached via react was indeed called so it behaves like I would expect if someone clicked on the element. I have not tested onChange but it should work, and not sure how this will fair in really old versions of IE but I believe the MouseEvent is supported in at least IE9 and up.

I eventually moved away from this for my particular use case because my component was very small (only a part of my application used react since i'm still learning it) and I could achieve the same thing another way without getting references to dom nodes.

UPDATE:

As others have stated in the comments, it is better to use this.refs.refname to get a reference to a dom node. In this case, refname is the ref you attached to your component via <MyComponent ref='refname' />.

At least on text inputs, it appears that onChange is listening for input events:

var event = new Event('input', { bubbles: true });
element.dispatchEvent(event);