<form onSubmit={this.handleSubmit}>
 <input type="text" placeholder="userName"/>
 <input type="text" placeholder="repo"/>
 <button type="submit">Go</button>
</form>

import { browserHistory } from 'react-router'

// ...
 handleSubmit(event) {
  event.preventDefault()
  const userName = event.target.elements[0].value
  const repo = event.target.elements[1].value
  const path = `/repos/${userName}/${repo}`
  browserHistory.push(path)
 },

export default React.createClass({

 // ask for `router` from context
 contextTypes: {
  router: React.PropTypes.object
 },

 handleSubmit(event) {
  // ...
  this.context.router.push(path)
 },
})