Евгений

'use strict';

const url = 'https://www.instagram.com/p/BGrZOf5OTpH/?taken-by=...';
const id = url.split('/')[4];

console.log(id); // => BGrZOf5OTpH

'use strict';

let cache = {};
let url = '/index.php?page=1';

const page = document.querySelector('.page');

if (!cache[url]) {
    fetch(url)
        .then((response) => {
            return response.text();
        })
        .then((data) => {
            cache[url] = data;
            page.innerHTML = data;
        });
} else {
    page.innerHTML = cache[url];
}

var total_price = null;

$(document).on('change', 'input.itemsInv', function(){
    //...
    total_price = parseFloat($(".Q131bgfh4vn").text());
    //...
});

$("#sendTradeOfferForPay").on('click', function(){
    //...
    data: {items: items, total: total_price, steamid: $("#itemsContainer").data('steamid'), token: $("#itemsContainer").data('token')   },
    //...
});

socket.on('trade_created', function(data){
    var trade = JSON.parse(data);
    var tradenumber = trade.tradeid;

    if (tradenumber) {
        $('#timevalue').addClass('invisible');
        $(".tradeOfferResponse").show().find('a').prop("href", "https://steamcommunity.com/tradeoffer/"+ tradenumber +"/");
    }
});

$(document).on('click', '.second_class', function () {
    //...
});

var triggers = document.querySelectorAll('.trigger');
var items = document.querySelectorAll('.list_inner');

[].forEach.call(triggers, function (trigger, index) {
    trigger.addEventListener('click', function () {
        items[index].classList.toggle('visible');
    });
});

function replaceReverse(string, reg, rep) {
    string = string.split('').reverse().join('');
    return string.replace(reg, rep);
}

function isEven(n) {
    if (n % 2 == 0)
        return true;

    return false;
}

<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 20 20" preserveAspectRatio="none"><polyline points="20 20 0 20 0 0 " fill="#000000" fill-rule="evenodd"/></svg>

<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 20 20" preserveAspectRatio="none"><polyline points="20 0 20 20 0 20 " fill="#000000" fill-rule="evenodd"/></svg>