How to use ternary operator for a return in JS?

Question

I have a function to check sums in an array :

function checkSum(array, sum) {
   // array = [1,4,6,11]  sum = 10
   var answers = [];
   var map = new Map();

   for (var x = 0; x < array.length; x++) {
       if (map.has(array[x])) {
           answers.push([sum - array[x], array[x]])
       } else {
           map.set(sum - array[x])  
       }
   }


   answers.length != 0 ? console.log(answers) : console.log("nada")
}

I originally had the last line just return answers; but let's say I don't want to return an empty array -- instead, I'd rather just log a statement.

why doesn't a return in a ternary conditional work such as this:

answers.length != 0 ? return answers : console.log("nada")

Answer 1

You need to use return answers.length != 0 ? answers : console.log("nada"). The reason it fails is because ternary conditions do not support return in their conditions. Infact, the ternary operator evaluates to an expression and expressions do not contain a return statement.

function checkSum(array, sum) {
  // array = [1,4,6,11]  sum = 10
  var answers = [];
  var map = new Map();

  for (var x = 0; x < array.length; x++) {
    if (map.has(array[x])) {
      answers.push([sum - array[x], array[x]])
    } else {
      map.set(sum - array[x])
    }
  }


  return answers.length != 0 ? answers : console.log("nada")
}

console.log(checkSum([1, 4, 6, 11], 10));

Answer 2

The ternary (conditional) operator expects the "expr1" part (where return answers is) to be an expression - that is, something that can be evaluated to a value, which can be used in other expressions. But a return statement is a statement, one which cannot possibly be interpreted as value, or as an expression; hence, a syntax error is thrown.

Instead of

answers.length != 0 ? console.log(answers) : console.log("nada")

either use a standard if statement:

if (answers.length !== 0) return answers;
console.log('nada');

or, if you just want to log, put the conditional operator inside the console.log instead:

console.log(
  answers.length === 0
  ? 'nada'
  : answers
)