ES6: Use the Rest Operator with Function Parameters

JavaScript
1

This code does not work for the instance where the “” argument is passed into sum. Please explain why.

function sum (...args){  //creates sum function
  if (args === ""){             //determines if argument passed is null
    return 0; //returns 0
  } else {
    return args.reduce((a, b) => a + b); returns sum of all arguments passed into sum
  }
}
3

The code I have written passes all parameters except the following:

sum();

I guess first question, if this argument is not null then what is it? (https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/null)

5

I thought so but then my problem is still the aforementioned condition:

function sum (...args){  
     return args.reduce((args = 0, b) => args + b); 
}
function summ(...args) {
    return args.reduce((a, b) => {
      return a + b;
    });
  }
}

I have tried both of these lines of code and am still getting errors with

sum();
7

Let me try to explain how I am looking at this so you can tell me what I don’t understand:

var arr1 = [1, 2, 3, 6];
const sum = (a, b) => a +b;
arr1.reduce(sum, 4); //16

This is because the reduce function is applying the sum function to all elements of arr1 and the initial value, 4.
Now applied:

function sum (...args){  //creates sum
     const add = (c, d) => c + d;  //creates add
  return args.reduce((add, b = 0) => add + b);  //runs add and reduce functions on the array args, initial value is 0
}
console.log(sum(12,2)); //14
console.log(sum()); //Error: Reduce of empty array with no initial value

It is because of this error that I tried using the if statement to filter out the condition to at the beginning.

9

Thank you very much @camperextraordinaire!