Web applications with server-side code written in JavaScript are getting increasingly more widespread nowadays. It is interesting to compare performance of a mature Java-based web server to a server based on relatively young Node.js JavaScript runtime.

Tomcat is the simplest and most popular among Java web servers. Basically it is an application executing Java web applications. The deployed applications use the implemented by Tomcat API for handling HTTP requests. Tomcat and Java existed before Node.js was developed but nowadays Node.js-based web applications are more widespread than the ones served by Tomcat or, perhaps, all the web applications written in Java…

Let’s make simple tests to figure out what is the best place for a script tag.

In a browser JavaScript can be used to do many things, but usually the primary task of JavaScript is generation of interactive content or, in other words, dynamic construction of the DOM. Considering that, what place in a HTML file is most suitable for a script tag? There are two reasonable options —before or after the rendered HTML. …

Testing in a browser simplifies the development of web applications. But how to mock module dependencies in a browser?

Testing in a browser saves time, particularly during prototype development. For uncomplicated modules, for example user-interface-related, it is possible to complete the code and then to write tests.

But imagine a module that performs sophisticated calculations. For example, a module that transforms and aggregates some complex statistics into simple data that can be plotted in a chart. During the development of complex calculations that you cannot do in your head, lots of debugging is inevitable and therefore frequent tests are indispensable.

…

You cannot do without import maps if during development you do not want to lose time on bundling.

Problems with URLs as module specifiers

import statement imports live bindings from the module indicated with a module specifier:

import defaultExport from 'moduleSpecifier';

When browsers started to support ES modules, only valid URLs were accepted as module specifiers. Recently implemented import maps extended the choice of specifiers. To appreciate how import maps facilitate JavaScript development, let’s first review the limitations and advantages of URLs in the role of module specifiers. …

JavaScript modules export values as live bindings except with export default.

What live binding are

JavaScript modules export values as live bindings. The term live binding means the reference to the memory location where the exported value is stored. In other words, the exported value is passed by reference to the module importing it. Except in live bindings, variables are never passed by reference in JavaScript.

Properties of live bindings

I use two simple modules to demonstrate the properties of live bindings.

The child module child.js exports variable as its default export:

// child.js
let variable = "value";
export { variable as default };

The parent module parent.js…

Lately it is possible without top level await for fetch.

Why to load a JSON as a module?

JSON modules are intended for the applications made up of JavaScript modules. JSON modules allow loading static or dynamically generated data during loading of JavaScript modules. With JSON modules ES modules got less inferior to AMD modules.

There might be many use cases for JSON modules, but I will describe how they simplify a task that I regularly face. In some web applications the start page layout or contents depend on some settings, for example the user privileges or preferences. …

Developers use them only in documentation, they are more user-friendly than links with tag ids.

When you click a link, the browser usually displays the top of the target page. If a link additionally includes the id of an HTML tag in the target page, the browser will scroll the loaded page to the specified tag. For example, if you click a link https://marian-caikovski.medium.com/uninstall-any-preinstalled-system-app-from-android-cell-phone-2f3dc47f69e0#d617, the browser will load the page and then will scroll it down so that the paragraph with obscure id d617 is shown in the top of the window.

In JavaScript logical operators AND and OR are used not only in conditions. They also serve as shortcuts for conditional statements.

&&, || and ?? operators return one of the two values used as their operands. The values can be of any type.

&&

value1 && value2 results in value2 when value1 is truthy and in value1 when value1 is falsy:

console.log(undefined && 'a'); //undefined
console.log(0 && 1); //0
console.log('a' && 'b'); //b

Basically, && is a shortcut for a function with a if statement:

function and(value1, value2) {
    if (value1) return value2;
    else return value1;
}

If the function and…