Set a cookie to expire tomorrow. Check for it's existance on run, and update content if cookie is already set.

write-cookie.js

// Prevents person from taking the same Survey twice

// Checks for cookie existance
var getCookie = function (name) {
    var value = "; " + document.cookie;
    var parts = value.split("; " + name + "=");
    if (parts.length == 2) return parts.pop().split(";").shift();
};

// Writes a cookie that expires tomorrow
function createCookie(name,value,path) {
    var expires = "";
    var date = new Date();
    var tomorrow = new Date(date.getFullYear(), date.getMonth(), date.getDate(), 23, 59, 59);
    expires = "; expires=" + tomorrow.toGMTString();
    if (!path) {
        path = "/";
    }
    document.cookie = name + "=" + value + expires + "; path=" + path;
}


// Assign a variable for our cookie
var surveyTaken = getCookie("_surveyCookie")

// If cookie exists, remove the ability to take the quiz again
if(surveyTaken == undefined){
	// They haven't taken the quiz, so move on!
    console.log("Survey not taken");

    // Write the cookie now.
    createCookie("_surveyCookie","completed")

} else{ 
    // They have taken the Survey already, show denied message 
	console.log("Survey already taken");

    // Hide the form for folks who've already submitted the form
    var surveyContent = document.getElementById("formContainer");
    surveyContent.innerHTML = '<section class="page-layout__section"><strong>We have received your survey submission. Thank you for the feedback. For additional feedback, please <a href="/contact">Contact Us</a>.</section>';
};