JavaScript cheat sheet

Locating DOM elements

// Get element by identifier.
let root = document.getElementById('uniqueidentifier');

// Get element within another element by attribute.
let widget = querySelector('[data-widget="widgetname"]');

// Find all elements within another element and do something with them.
let missingItems = root.querySelectorAll(':scope [data-region="itemname"].missing');
missingItems.forEach(item => {
    window.console.log(item);
});

// Find the closest parent element matching the selector.
let region = widget.closest('[data-region]');

CSS classes

// Check if the element has a certain class.
if (e.target.classList.contains('classname')) {

    // Add a new CSS class to the element.
    e.target.classList.add('someclassname');

    // Remove a CSS class from the element.
    e.target.classList.remove('anotherclassname');
}

Custom events (core/pubsub)

import * as PubSub from 'core/pubsub';

let eventName = 'tool_jsdemo/modulename:eventname';

// Subscribe as the event handler.
PubSub.subscribe(eventName, data => {
    window.console.log(data);
});

// Trigger the event with custom data passed to the subscribers.
let data = {};
PubSub.publish(eventName, data);

Strings (core/str)

import * as str from 'core/str';

str.get_string('identifier', 'tool_jsdemo').then((text) => {
    window.console.log(text);
});

import {get_string as getString} from 'core/str';

const sayHello = async () => {
    window.console.log(await getString('identifier', 'tool_jsdemo'));
}