Validate text entry based on minimum number of words (not characters)

I have a text entry field where respondents must enter a minimum of 100 words (not characters). I'm using the following JavaScript (in add.OnReady) to count and display the number of words entered in the text box. I want to set up a validation that checks to see if the the user has written at least 100 words, effectively preventing them from moving to the next block until they meet the minimum.

var display = $('ACT1_wordCountDisplay');
var questionID = this.questionId;
var textbox =$('QR~' + questionID);
var that = this;
function countWords(s){
s = s.replace(/\\n/g,' '); // newlines to space
s = s.replace(/(^\\s*)|(\\s*$)/gi,''); // remove spaces from start + end
s = s.replace(/[ ]{2,}/gi,' '); // 2 or more spaces to 1
if(s == ''){
return 0;
}else{
return s.split(' ').length;
}
}

textbox.onkeyup = function(e){
display.update(countWords(textbox.value));
console.log(textbox.value);
}