I want to cut this paragraph after certain number of words, not characters

const Text = "But I must explain to you how all this mistaken idea of denouncing pleasure and praising pain was born and I will give you"

For instance: if i do

Text.substring(0,50)

the output will be

'But I must explain to you how all this mistaken id'

the word "idea" is cut and is not what I want, i want the whole word and then maybe add " . . . "

example 'But I must explain to you how all this mistaken idea . . .'