Javascript Question posted in
A very good W3school tutorial can be found here.

Javascript – Is there a way to achieve currying with a local variable

We need to create a function that would print the results for:
console.log(sum(1)(2)(3)(4)(5)(6)());

So this is how I did:

let res = 0;
function sum(a){
  if(a){
    res = res + a;
    return sum; //Return the same function for next chain of actions
  }else{
    return res;
  }

}
console.log(sum(1)(2)(3)());

Is there a way I can achieve this with a local res? the problem I face with making it local is, it just gets reset in the next call.

I see some solutions like this:

function sum(a) {
  return function(b){
    if(!b){
        return a;
    }
    return sum(a+b);
  }
}

But the way I did appears more natural and intuitive to me and I just want to make that work with res as local instead of gloabl.

Tags:

2

Answers


  1. 0

    You could do it like this:

    The innerSum function maintains a closure over res. This allows res to retain its value across multiple calls to innerSum.

    function sum(a) {
  let res = a;
  function innerSum(b) {
    if (b !== undefined) {
      res += b;
      return innerSum;
    } else {
      return res;
    }
  }
  innerSum.toString = function() {
    return res;
  };
  return innerSum;
}

    Demo

    function sum(a) {
  let res = a;
  function innerSum(b) {
    if (b !== undefined) {
      res += b;
      return innerSum;
    } else {
      return res;
    }
  }
  innerSum.toString = function() {
    return res;
  };
  return innerSum;
}

console.log(sum(1)(2)(3)(4)(5)(6)().toString());
    Login or Signup to reply.
  2. 0

    You can make the sum an IIFE and put res in the local scope. After that, when called with no arguments, reset the res to 0 to make it ready for the next call.

    const sum = (() => {
  let res = 0;
  
  return function (a) {
    if (typeof a === 'number') {
      res = res + a;
      return sum;
    } else {
      const temp = res;
      res = 0;
      return temp;
    }
  }
})();

console.log(sum(1)(2)(3)());
console.log(sum(1)(2)(3)(4)());

    It can also be shortened in a simpler but maybe cursed syntax:

    const sum = (res => a => {
  if (typeof a === 'number') {
    res = res + a;
    return sum;
  }
  
  try {
    return res;
  } finally {
    res = 0;
  }
})(0);

console.log(sum(1)(2)(3)());
console.log(sum(1)(2)(3)(4)());
    Login or Signup to reply.
Please signup or login to give your own answer.

Back To Top
Search