JSFiddle - React, Tailwind, and code Playground

by radu

HTML

<input type="text" id="user_input"/>
<p id="price_output"></p>

JavaScript

$(function() {
    var tier_prices = [
        [100, 20],
        [200, 15],
        [500, 10]
    ];

    $('#user_input').change(function() {
        var num = parseInt($(this).val(), 10),
            price = 0,
            n = tier_prices.length - 1;

        if (num > tier_prices[n][0]) {
            price = tier_prices[n][1];   
        } else {
            for (var i = 0; i <= n; i++) {                   
                if (num <= tier_prices[i][0]) {
                    price = tier_prices[i][1];
                    break;
                }
            }
        }

        $('#price_output').text(price * num);
    });
});