React.js: submit form programmatically does not trigger onSubmit event

I have success with this. This triggers the handleSubmit upon clicking. Hope this helps.

<form
  onSubmit={this.handleSubmit}
  ref={ (ref) => { this.form = ref; } }
>
    <a onClick={ () => { this.form.dispatchEvent(new Event('submit')) } }>
        Validate
    </a>
</form>

Found from here: https://github.com/facebook/react/issues/6796

Update 2021

The solution from the accepted answer didn't work for me so I decided to update this topic.

React 16 (and older)

In the original answer, the second parameter of the Event constructor is missing. Without {cancelable: true} parameter, the preventDefault() method cannot be run.

<div>
    <form onSubmit={e => e.preventDefault()} ref={ref => this.form = ref}>
        <input name="tmp" />
    </form>

    <button onClick={e => this.form.dispatchEvent(
        new Event("submit", { cancelable: true })
    )}>
        Submit form
    </button>
</div>

React 17 (and probably newer versions in the future)

In the current version of React (17), there has been a quire big change in event delegation (details here). Thus, the solution above needs a small improvement to work with this version of the library. This change is the bubbles: true parameter. Working code would look like this:

<div>
    <form onSubmit={e => e.preventDefault()} ref={ref => this.form = ref}>
        <input name="tmp" />
    </form>

    <button onClick={e => this.form.dispatchEvent(
        new Event("submit", { cancelable: true, bubbles: true })
    )}>
        Submit form
    </button>
</div>