Interesting code snippets to talk about

interview-snippets.js

// -------------------------------------------------------------------------------------------------------
// Once (from source of async)
// @see https://github.com/caolan/async/blob/f5d86b80b986c8cad88a224a6f8b3ec154839490/lib/internal/once.js
// -------------------------------------------------------------------------------------------------------

function once(fn) {
    return function () {
        if (fn === null) return;
        var callFn = fn;
        fn = null;
        callFn.apply(this, arguments);
    };
}

// -----------------------------------------------------
// dlv() source
// https://github.com/developit/dlv/blob/master/index.js
// -----------------------------------------------------

export default function dlv(obj, key, def, p) {
    p = 0;
    key = key.split ? key.split('.') : key;
    while (obj && p<key.length) obj = obj[key[p++]];
    return obj===undefined ? def : obj;
}

// ------------------------------
// UMD (simplified rollup output)
// ------------------------------

(function (global, factory) {
    typeof exports === 'object' && typeof module !== 'undefined' ? module.exports = factory(require('myLibrary')) :
    typeof define === 'function' && define.amd ? define(['myLibrary'], factory) : (global.MyMod = factory(global.MyLibrary));
}(this, (function (myLibrary) {
    const myMod = { doSomething: function() { myLibrary.coolHelper(); } }
    return myMod;
})));

// -------------------------------
// Google Tag Manager (beautified)
// -------------------------------

(function(w, d, s, l, i) {
    w[l] = w[l] || [];
    w[l].push({
        'gtm.start': new Date().getTime(),
        event: 'gtm.js'
    });
    var f = d.getElementsByTagName(s)[0],
        j = d.createElement(s),
        dl = l != 'dataLayer' ? '&l=' + l : '';
    j.async = true;
    j.src = 'https://www.googletagmanager.com/gtm.js?id=' + i + dl;
    f.parentNode.insertBefore(j, f);
})(window, document, 'script', 'dataLayer', 'GTM-XXXX');

// ---------------------------
// request logger (simplified)
// ---------------------------

logger.requestLogger = (req, res, next) => {
  req._startTime = Date.now()
  const end = res.end
  res.end = (chunk, encoding) => {
    const responseTime = Date.now() - req._startTime
    res.end = end
    res.end(chunk, encoding)
    logger.labeledInfo(req.method, `${req.originalUrl || req.url} ${responseTime}ms`)
  }
  next()
}