Sorting an Array using .sort in an function equals Undefined in JavaScript

Question

I want to create a new array that is copy of mine array and at the same time sort it using the value stored in numTeeth. I'm using the function sort to accomplish this task. The problem is that if I try to debug it using a console log it show as result the undefined value.

const speciesArray = [ 
  {speciesName:'shark', numTeeth:50}, 
  {speciesName:'dog', numTeeth:42}, 
  {speciesName:'alligator', numTeeth:80}, 
  {speciesName:'human', numTeeth:32}
  ];

const sortSpeciesByTeeth = arrayIn => {
  arrayIn.sort( function (a, b) {
    return a.numTeeth - b.numTeeth;
  });
}

console.log(sortSpeciesByTeeth(speciesArray))

While if I use the same code without declaring it as separate function it works despite it sort the original array. What I don't want in the final code. Example

const speciesArray = [ 
  {speciesName:'shark', numTeeth:50}, 
  {speciesName:'dog', numTeeth:42}, 
  {speciesName:'alligator', numTeeth:80}, 
  {speciesName:'human', numTeeth:32}
  ];

speciesArray.sort( function (a, b) {
  return a.numTeeth - b.numTeeth;
});

console.log(speciesArray)

You need to return the result array from `sortSpeciesByTeeth ` function — sojin, Nov 14 '21 at 07:19

score 1 · Accepted Answer · answered Nov 14 '21 at 07:22

1) You have to return something from the function sortSpeciesByTeeth, by default undefind is returned.

2) If you want a copy of original array then you can use spread syntax

The sort() method sorts the elements of an array in place and returns the sorted array. - MDN

const sortSpeciesByTeeth = (arrayIn) => {
  return [...arrayIn.sort((a, b) => a.numTeeth - b.numTeeth)];
};

or

const sortSpeciesByTeeth = (arrayIn) => [
  ...arrayIn.sort(({ numTeeth: nT1 }, { numTeeth: nT2 }) => nT1 - nT2),
];

const speciesArray = [
  { speciesName: "shark", numTeeth: 50 },
  { speciesName: "dog", numTeeth: 42 },
  { speciesName: "alligator", numTeeth: 80 },
  { speciesName: "human", numTeeth: 32 },
];

const sortSpeciesByTeeth = (arrayIn) => {
  return [
    ...arrayIn.sort(function (a, b) {
      return a.numTeeth - b.numTeeth;
    }),
  ];
};

console.log(sortSpeciesByTeeth(speciesArray));

/* This is not a part of answer. It is just to give the output full height. So IGNORE IT */
.as-console-wrapper { max-height: 100% !important; top: 0; }

inordirection · Answer 2 · 2021-11-14T07:28:40.093

In a JS arrow function, the first statement is only implicitly returned if your function body is not wrapped in braces. This means sortSpeciesByTeeth is not returning anything. You need to just add a return statement:

const speciesArray = [ 
  {speciesName:'shark', numTeeth:50}, 
  {speciesName:'dog', numTeeth:42}, 
  {speciesName:'alligator', numTeeth:80}, 
  {speciesName:'human', numTeeth:32}
  ];

const sortSpeciesByTeeth = arrayIn => {
  return arrayIn.sort(function (a, b) {
    return a.numTeeth - b.numTeeth;
  });
}

console.log(sortSpeciesByTeeth(speciesArray))

Your original sortSpeciesByTeeth function was actually sorting the list, but it was just falling off the end without returning anything, therefore implicitly returning undefined to the console.log statement. (So if you sorted the array before logging it you would also have gotten the desired result):

const speciesArray = [ 
  {speciesName:'shark', numTeeth:50}, 
  {speciesName:'dog', numTeeth:42}, 
  {speciesName:'alligator', numTeeth:80}, 
  {speciesName:'human', numTeeth:32}
  ];

const sortSpeciesByTeeth = arrayIn => {
  arrayIn.sort(function (a, b) {
    return a.numTeeth - b.numTeeth;
  });
}

sortSpeciesByTeeth(speciesArray)
console.log(speciesArray)

Sorting an Array using .sort in an function equals Undefined in JavaScript

2 Answers2