It is just a new ES6 syntax, which simplifies creating properties on the literal syntax

In short, if the name is the same as the property, you only have to write it once

So this would be exactly the same :)

function addTodoWithDispatch(text) {
  const action = {
    type: ADD_TODO,
    text: text
  }
  dispatch(action)
}

In the above code

function addTodoWithDispatch(text) {
  const action = {
    type: ADD_TODO,
    text
  }
  dispatch(action)
}

here text is an example of object literal shorthand notation. ES6 gives you a shortcut for defining properties on an object whose value is equal to another variable with the same key.

As has been said this is just shorthand for writing

const action = {
    type: ADD_TODO,
    text: text
  }
  dispatch(action)

Have a look at this blog

If you look at the next page in document http://redux.js.org/docs/basics/Reducers.html

function todoApp(state = initialState, action) {
 switch (action.type) {
  case SET_VISIBILITY_FILTER:
  return Object.assign({}, state, {
    visibilityFilter: action.filter
  })
 case ADD_TODO:
  return Object.assign({}, state, {
    todos: [
      ...state.todos,
      {
        text: action.text,
        completed: false
      }
    ]
  })
case TOGGLE_TODO:
  return Object.assign({}, state, {
    todos: state.todos.map((todo, index) => {
      if(index === action.index) {
        return Object.assign({}, todo, {
          completed: !todo.completed
        })
      }
      return todo
    })
  })
default:
  return state
 }
}

It is expecting property name text. As @Icepickle mentioned it is a valid format but you can also change to below format:

function addTodoWithDispatch(text) {
  const action = {
     type: ADD_TODO,
     text:text
   }
  dispatch(action)
}