Sort a JavaScript array by some boolean operation

UPDATE Feb 4, 2022 Yes, as commenter Matthias pointed out, you can let JavaScript implicitly make the conversion of boolean minus boolean to end number a number of -1, 0, or 1.

Original but edited blog post below...

Imagine you have an array like this:

const items = [
  { num: 'one', labels: [] },
  { num: 'two', labels: ['foo'] },
  { num: 'three', labels: ['bar'] },
  { num: 'four', labels: ['foo'] },
  { num: 'five', labels: [] },
];

What you want, is to sort them in a way that all those entries that have a label foo come first, but you don't want to "disturb" the existing order. Essentially you want this to be the end result:

{ num: 'two', labels: ['foo'] },
{ num: 'four', labels: ['foo'] },

{ num: 'one', labels: [] },
{ num: 'three', labels: ['bar'] },
{ num: 'five', labels: [] },

Here's a way to do that:

items.sort(
  (itemA, itemB) =>
    itemB.labels.includes('foo') - itemA.labels.includes('foo')
);
console.log(items);

And the outcome is:

[
  { num: 'two', labels: [ 'foo' ] },
  { num: 'four', labels: [ 'foo' ] },
  { num: 'one', labels: [] },
  { num: 'three', labels: [ 'bar' ] },
  { num: 'five', labels: [] }
]

The simple trick is to turn then test operation into a number (0 or 1) and you can do that with Number.

Boolean minus boolean is operator overloaded to become an integer. From the Node repl...

> true - false
1
> false - true
-1
> false - false
0
> true - true
0