Deno.md

Deno Reference Notes

Useage notes for deno.

Events

Deno uses the same API as in the web browser, events are managed using Event or CustomEvent and EventTarget.

• MDN: EventTarget
• MDN: Event
• MDN: CustomEvent (Supports Passing Data)

Note: The CustomEvent constructor requires an object with a detail attirbute as you can see below. Read more on the Mozilla documentation.

Using EventTarget as a separate object:

const et = new EventTarget()
et.addEventListener('this-event', (e) => {
  console.log('Event raised.', e)
})
et.dispatchEvent(new Event('this-event'))

Inheriting from EventTarget:

class Car extends EventTarget {
  startEngine() {
    this.dispatchEvent(new Event('start-engine'));
  }
  revEngine() {
    const evt = new CustomEvent('rev-engine', { detail: { rpm: 2000 } });
    this.dispatchEvent(evt);
  }
}

const car = new Car();
car.addEventListener('start-engine', (e) => {
  console.log('Engine started and running...', e);
});
car.addEventListener('rev-engine', (e) => {
  console.dir(e)
  console.log('Engine revved - RPM:', e.detail.rpm);
});

car.startEngine();
car.revEngine();

ErrorEvent:

const error = new ErrorEvent('a message', {
    error : new Error('original error'),
    message : 'another message',
    lineno : 123,
    filename : 'index.js'
});

Reading JSON Files

Because deno can't import json files, you need to use the full path to the file and the readJsonSync and path standard modules.

import { readJsonSync } from "https://deno.land/std/fs/mod.ts";
import * as path from "https://deno.land/std/path/mod.ts";
const pwd = path.fromFileUrl(path.dirname(import.meta.url));
const join = (p) => path.join(pwd, p);
const jsonSchema = readJsonSync(join("./schema.json"));

Module Name

Unfortunately, Deno.cwd does not work from inside imported modules. It only shows the working directory of the current application.

On the positive side, Deno supports the ESM import.meta.url attribute, so you can extract the information.

import * as path from "https://deno.land/std/path/mod.ts";
const ext = path.extname(import.meta.url);
const moduleName = path.basename(import.meta.url, ext);