How does JS sort an array of objects without a compare function?

Question

As per the title, how does JS sort an array of objects without using a compare function?

For example:

const bookshops = [{
  id: 3,
  name: 'bookshop3',
  imgSrc: 'https://www.google.com/'
}, {
  id: 8,
  name: 'bookshop8',
  imgSrc: 'https://www.google.com/'
}, {
  id: 2,
  name: 'bookshop2',
  imgSrc: 'https://www.google.com/'
}, {
  id: 9,
  name: 'bookshop9',
  imgSrc: 'https://www.google.com/'
}, {
  id: 4,
  name: 'bookshop4',
  imgSrc: 'https://www.google.com/'
}, {
  id: 6,
  name: 'bookshop6',
  imgSrc: 'https://www.google.com/'
}, {
  id: 10,
  name: 'bookshop10',
  imgSrc: 'https://www.google.com/'
}, {
  id: 7,
  name: 'bookshop7',
  imgSrc: 'https://www.google.com/'
}];

bookshops.sort();

console.log(bookshops);

What will be the output? Did "bookshops" get sorted?

"What will be the output?" impossible to say, as it will be implementation dependent. There is a high chance that nothing will change but you cannot rely on it. The default comparison is just lexicographical. Converting objects to a string produces "[object Object]" for each of them, so technically they'd all be equal. — VLAZ
– VLAZ, Commented Feb 9, 2021 at 7:33
Read about sort function here developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/… — Hassan Imam
– Hassan Imam, Commented Feb 9, 2021 at 7:34

Kiong · Accepted Answer · 2021-02-09 07:49:05Z

Special thanks to @VLAZ & @Hassan Imam for showing me the answer.

To make it clearer to anyone who comes by to view this question:

Javascript sort comparison function is lexicographical. Which means that if you do not pass in a compare function:

xxx.sort()

The sort will compare the lexicographical value of each value in the array.

As per the specifications here:

If compareFunction is not supplied, all non-undefined array elements are sorted by converting them to strings and comparing strings in UTF-16 code units order. For example, "banana" comes before "cherry". In a numeric sort, 9 comes before 80, but because numbers are converted to strings, "80" comes before "9" in the Unicode order. All undefined elements are sorted to the end of the array.

To illustrate further:

const list = [80, 9];
list.sort();
console.log(list); // [80, 9] <= its not [9, 80]

In conclusion, always use a compare function

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