Check if a path is relative

JavaScript

const isRelative = (path) => !/^([a-z]+:)?[\\/]/i.test(path)

TypeScript

const isRelative = (path: string): boolean => !/^([a-z]+:)?[\\/]/i.test(path)

Examples

isRelative('/foo/bar/baz') // false
isRelative('C:\\foo\\bar\\baz') // false
isRelative('foo/bar/baz.txt') // true
isRelative('foo.md') // true