Automagically append arguments to function calls or add to `this` within function

appendArguments.js

/* Append arguments to functions */
function appendArguments(fn, append, context) {
  if (!append) return fn
  // console.log('context', context)
  return function () {
    /* Original args */
    const args = Array.prototype.slice.call(arguments)
    // console.log('original args', arguments)
    
    /* Create clone of args */
    let newArgs = new Array(fn.length)
    for (let i = 0; i < args.length; i++) {
      newArgs[i] = args[i]
    }
    
    /* Append new arg to end */
    newArgs[newArgs.length] = append
    // console.log('newArgs', newArgs)
    return fn.apply(context, newArgs)
  }
}

function getLastArg(args) {
  return args[args.length - 1]
}

function normalFunction(a, b) {
  console.log('Function this', this)
  console.log('Function arguments', arguments)
  console.log('Function arg a', a)
  console.log('Function arg b', b)
  const lastArg = getLastArg(arguments)
  // const lastArg = arguments[arguments.length - 1]
  console.log('Function lastArg', lastArg)
}

var arrowFunction = (a, b, ...args) => {
  console.log('ArrowFunction arg a', a)
  console.log('ArrowFunction arg a', b)
  const lastArg = getLastArg(args)
  console.log('ArrowFunction lastArg', lastArg)
}

var argToAppend = 'add-this-arg'
var newThis = { funky: 'hi' }

var extendedFunction = appendArguments(normalFunction, argToAppend, newThis)

extendedFunction(1, 2)

var extendedArrowFunction = appendArguments(arrowFunction, argToAppend)

extendedArrowFunction(3, 4)

/**
 * Rebinding Arrow functions
 */

function isArrowFunc(func){
  return typeof func === 'function' && func.toString().indexOf("=>") > -1
}

// unsafe rebind arrow function
function arrowBind(context, fn) {
  let arrowFn = fn;
  (function() {
    try { 
      arrowFn = eval(fn.toString())
    } catch (e) {}
  }).call(context)
  return arrowFn
}

var preBoundArrow = () => {
  console.log(this)
}

preBoundArrow()

var newThisForArrow = { cool: 'hello'}
var reBound = arrowBind(newThisForArrow, preBoundArrow)

reBound()