trim whitespace from start and end of lines in multiline strings in js/ts

linetrim.ts

// This little function joins strings[0] with the l-r-... zip of strings.slice(1) and expr

// TypeScript
export const linetrim = (strings: TemplateStringsArray, ...expr: string[]): string => {
    return strings.slice(1).reduce((str, fragment, i) => str + expr[i] + fragment, strings[0]).replace(/^.*$/gm, line => line.trim() + `\n`)
}

// JavaScript
export const linetrim = (strings, ...expr) => {
    return strings.slice(1).reduce((str, fragment, i) => str + expr[i] + fragment, strings[0]).replace(/^.*$/gm, line => line.trim() + `\n`)
}

// Usage

const a = linetrim`this
    is
    a
    multiline
    string`

const b = linetrim`this
is
a
multiline
string`

expect(a).toBe(b) // passes