promise is a returned object representing the eventual completion or failure of an asynchronous operation, to which you can attach callbacks, as opposed to passing callbacks into a function. Declaring a function
async further simplifies the syntax, allowing you to use
await within the function to pause in a non-blocking way until the promise settles.
Typed arrays are an ES6 API for handling binary data, something Node.js could have used; the lack of binary data support led to some Node.js design issues. Deno uses typed arrays when it needs to manipulate raw binary data. Node.js now supports typed arrays for user code.
Node.js design shortcomings
According to Dahl, who after all did design both Node.js and Deno, Node.js suffers from three major design issues:
- a poorly designed module system, with centralized distribution;
- lots of legacy APIs that must be supported;
- and a lack of security.
Deno fixes all three problems.
Deno secure execution
The way Deno improves security over Node.js is simple: By default, Deno won’t let a program access disk, network, subprocesses, or environmental variables. When you need to allow any of these, you can opt in with a command line flag, which can be as granular as you like, for example
--allow-net=google.com. Another security improvement in Deno is that it always dies on uncaught errors, unlike Node.js, which will allow execution to proceed after an uncaught error, with results that may not be predictable.
In Node.js, you load CommonJS modules using the
require keyword and they all, standard and third-party alike, implicitly come from npmjs.com. In Deno, you load ES modules using the
import keyword and explicitly state the URL. For example:
import * as log from "https://deno.land/std/log/mod.ts";
Deno modules can be hosted anywhere – there is no centralized repository for third-party modules. In addition, modules are always cached and compiled locally, and aren’t updated unless you explicitly ask for a refresh. Therefore, you should be able to run Deno programs that are already on your laptop, as long as all the imports have been resolved once, even if you are on an airplane with no connectivity.
Deno does have a centralized collection of standard modules that do not have external dependencies and are reviewed by the Deno core team; it lives on the deno.land server. The deno_std module collection is a loose port of Go’s standard library.
There is a little history behind that choice of model for the library. Dahl wrote his prototype of Deno primarily in the Go language, but discovered potential conflicts between the garbage collectors in Go and V8. He and his collaborators then rewrote Deno proper with V8, Rust, and the Rust asynchronous I/O package Tokio. They implemented the Deno standard library in TypeScript.
At this point, Deno is a reasonable and fun environment to use for building small private scripting projects in TypeScript. According to Dahl, Deno will never really affect the success of Node.js. Nevertheless, once Deno reaches version 1.0 it may well become a viable choice for building larger projects.
This story, “What is Deno? A ‘better’ Node.js” was originally published by
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