leemorgan-dev/views/birthdayParadox/index.js

let partiers = 23;
let months = ["January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December"];

display = ()=>{
    let datesDiv = document.querySelector("#datesDiv");

    document.querySelector("#partiers").value = partiers;

    while(datesDiv.children.length > 0){
        datesDiv.removeChild(datesDiv.firstChild);
    }

    let nums = [];
    for(let i = 0; i < partiers; i++){
        let num = Math.floor((Math.random() * 366) + 1);
        if(num === 60){
            i--;
        }else{
            nums.push(num);
        }
    }

    let matches = [];
    for(let i = 0; i < nums.length; i++){
        for(let j = i + 1; j < nums.length; j++){
            if(nums[i] === nums[j]){
                matches.push(nums[i]);
                break;
            }
        }
    }

    for(let num of nums){
        let date = new Date(2020, 0);
        date = new Date(date.setDate(num));

        let para = document.createElement("p");
        para.classList = "date";
        para.innerText = `${months[date.getMonth()]} ${date.getDate()}`;
        datesDiv.appendChild(para);

        for(let match of matches){
            if(match === num){
                para.classList += " match";
                break;
            }
        }
    }

    calculateChance();
},

calculateChance = ()=>{
    let chance = document.querySelector("h3");
    let input = document.querySelector("#partiers");
    
    partiers = input.value;
    

    let percent = 1
    for(let i = 1; i < partiers; i++){
        percent *= (365 - i) / 365;
    }

    chance.innerText = `${((1 - percent) * 100).toFixed(4)}% chance of a match`;
}

document.getElementById("partiers").onchange = ()=>{calculateChance()};
document.getElementById("tryAgain").onclick = ()=>{display()};
display();