Action is an object. So whenever you dispatch actions, you’d have to give dispatch() an action object (with the type that we are expecting), like so:

dispatch({ type: 'DECREMENT' })

If you don’t save it like so

const DECREMENT = 'DECREMENT'

you are

• prone to typos and spelling errors
• you wouldn’t know which types exist because they haven’t been saved before hand (and so it wouldn’t autocomplete either)
• the next time you want to change an action type, you’d have to change it in place everywhere it’s used. If you save it as a contant, then you only update the constant in one place