Get a cookie by name in TypeScript

getCookie.ts

// Given a cookie key `name`, returns the value of
// the cookie or `null`, if the key is not found.
function getCookie(name: string): string {
	const nameLenPlus = (name.length + 1);
	return document.cookie
		.split(';')
		.map(c => c.trim())
		.filter(cookie => {
			return cookie.substring(0, nameLenPlus) === `${name}=`;
		})
		.map(cookie => {
			return decodeURIComponent(cookie.substring(nameLenPlus));
		})[0] || null;
}

Since the value could be null, you should define that in the return type ;)

getCookie(name: string): string|null {

Thanks for sharing!