bind.js

// Dhruven
// In the interview, I put myself in a rabbit hole
// with no possible solution
//
// What I was trying to do is to pass the arguments from the first
// function to the second function.
//
// The problem is the second function is return as a value
// therefore it is an independent function and there is no way for it to accept
// a value... The value needs to be passed as an argument by the executed function
//
// if you see below testFunC takes arguments and they are spread as
// 'input'
// the returned function can not accept first functions arguments as an argument
// that is why we have to use closure
//
// closure lets us remember the first functions variables and then pass them
// to the second returned function

function testFunC(...input) {
  const args = input
  return function(a, args) {
    console.log(args) // returns undefined
    return a
  }
}

const fnTestFunC = testFunC(6)
console.log(fnTestFunC(5))

// Using closure we can pass the arguments like below
function testFunD(input) {
  const b = input
  return function(a) {
    console.log(b) // returns 6
    return a + b // returns 11
  }
}

const fnTestFunD = testFunD(6)
console.log(fnTestFunD(5))

// ----------------------------
const obj = {
  a: 1,
  b: 2
}

function testFunE() {
  return this.a + this.b
}

console.log(testFunE()) // returns NaN
console.log(testFunE.bind(obj)()) // returns 3

// if we come back to what I was trying to do in the interview
// I was binding a function to an object and then executing it and
// assigning the returned value (which is a function) to a variable and
// then executing that variable with new parameters.
// below is how it shoould be done, the way I was trying was impossible as arguments
// can only be set by the executing function.


const objF = {
  a: 1,
  b: 2
}

function testFunF(...argsF) {
  const initialArgs = argsF
  const sum = this.a + this.b
  return function(a, b) {
    console.log(initialArgs)
    return a + b + sum + initialArgs[0] + initialArgs[1]
  }
}
const funTestFunF = testFunF.bind(objF)(3, 4)
console.log(funTestFunF(5, 6)) // returns 21

// I hope this explains why I was confused...
// Thanks