nodejs function().anotherFunction() how they do it? - node.js

Question

I install a library/module but I am curious how they do it
const modules = require('abc');
const app = new modules('123');
const client = app.f1('abcdef').f2('ghi');
console.log(client.to());
const client2 = app.f1('1111111').f2('2222');
console.log(client2.to());
console.log(client.to());
result is 123:abcdef-ghi
result is 123:1111111-2222
result is 123:abcdef-ghi
how they did it?
i want to create that example lib/module
please give me sample code

Answer 1

Depending on your exact requirements, something like this seems to work:
let state = Symbol("private")
class App {
constructor(arg) {
this[state] = arg
}
f1 = arg => new App(this[state] + ":" + arg)
f2 = arg => new App(this[state] + "-" + arg)
to = () => this[state]
}
Here each of the chainable method returns a new instance of the class, each keeping the temporary result as a local state. The to() method returns that state.

Answer 2

This is what I use for doing function().anotherFunction()
function func() {
console.log("ran func")
return {
"anotherFunc": function () {
console.log("ran another func")
}
}
}
func().anotherFunc()
You can also just return a object
const returnData = {
"anotherFunc": function () {
console.log("ran another func")
}
}
function func() {
console.log("ran func")
return returnData
}
func().anotherFunc()
Example of use:
function word1(in_1) {
return {
"word2": function (in_2) {
console.log(`Inputs: ${in_1} ${in_2}`)
}
}
}
word1("Hello").word2("World")
// Expected output: Inputs: Hello World