file-utility.js

/**
 * Function for reading files as promise.
 * @param {(reader: FileReader) => void} readCallback
 *   Execute the read, gets file reader as argument.  
 *   e.g. `r => r.readAsText(file)`
 * @returns {Promise<FileReader['result']>}
 *   Promise that resolves to the file reader result.
 */
export function readFile(readCallback)
{
	return new Promise((res, rej) =>
	{
		const reader = new FileReader();
		reader.onload = () => res(reader.result);
		reader.onerror = e => rej(reader.error);
		readCallback(reader);
	});
}

/**
 * Load an image as promise.
 * @param {string} src The source of the image.
 * @returns {Promise<HTMLImageElement>} Promise that resolves to the image object.
 */
export function loadImage(src)
{
	return new Promise((res, rej) =>
	{
		const img = new Image();
		img.onload = () => res(img);
		img.onerror = e => rej(e);
		img.src = src;
	});
}