React Form Component onSubmit Handler Not Working

For me, it was because the form didn't have an action property set.

<form onSubmit={this.handleSubmit} action="#">
    <input placeholder="githug login" ref="login" />
    <button>Add Login</button>
</form>

One obvious piece of information: do not forget to include your button inside the <form>. I got stuck for a while until I figured out I had put my submit button outside my form, like this:

  <form onSubmit={ this.handleSubmit }>
    <input placeholder="githug login" ref="login" />
  </form>            
  <button type="submit">Add Login</button>

hence the onSubmit event was not being called, and would never be.

When you use React with ES2015 classes you should set this to event handlers

class Form extends React.Component {
  constructor(props) {
     super(props);
     this.handleSubmit = this.handleSubmit.bind(this);
  }    

  handleSubmit(e) {
    e.preventDefault();

    let loginInput = this.refs.login;
    this.props.addCard(loginInput.value);
    loginInput.value = '';
  }

  render() {
    return(
      <form onSubmit={ this.handleSubmit }>
        <input placeholder="githug login" ref="login" />
        <button>Add Login</button>
      </form>
    );
  }
}

Example

No Autobinding

Methods follow the same semantics as regular ES6 classes, meaning that they don't automatically bind this to the instance. You'll have to explicitly use .bind(this) or arrow functions =>.

You need to use button or input with type="submit"

<button type="submit">Submit</button>

Or

<input type="submit" value="Submit" />