TS Flatten

interface ILayered extends Array<number | ILayered> { }
function flatten(flattenMe: ILayered) {
	const flat: number[] = [];
	const permeate = (layered: ILayered) => {
		layered.forEach((item) => {
			if(Array.isArray(item)) {
				permeate(item);
			} else {
				flat.push(item);
			}
		})
	}
	permeate(flattenMe);
	return flat;
}

Written in Typescript, uses recursive pattern.