exercise 5 in chapter 4

[ghost]

I think that this assertion function is comparing the array 'a' with the each elements of array 'b'.
So, I tried that the arguments [1], [1], [1] give to function is. The result was false.
I think that the result is true in this case.
Please tell me why this assertion function 'is' is correct?
I read this book in Japanese. If the translation is not good, could you tell me the sentences of the exercise 5 in English?

[bcherny]

Hey there! This example may be a little confusing -- is performs a shallow comparison, but the example might make it seem like we actually want a deep comparison.

This should work, since we're checking that each argument references the same value (it does):

let array = [1, 2]
console.log(is(array, array, array)) // true

This wouldn't work, because each array we pass in is a brand new reference:

console.log(is([1, 2], [1, 2], [1, 2])) // false

You could, of course, extend is to perform a deep comparison (let's call it looksLike). Want to try implementing it? Once you're done, it should work like this:

looksLike('a', 'a', 'a') // true
looksLike([1, [2]], [1, [2]], [1, [2]], [1, [2]]) // true
looksLike([1], [1], [2]) // false

[alexovn]

You just need to make something like this:

function is<T>(a: T, ...b: [T, ...T[]]): boolean {
  return b.every((_) => JSON.stringify(_) === JSON.stringify(a));
}

[alexovn]

More verbose variant:

function is<T>(
  a: T,
  ...b: [T, ...T[]]
): boolean {
  let c
  for(let i = 0; i < b.length; i++) {
    c = JSON.stringify(a) === JSON.stringify(b[i])
    return c
  }
  return c !== undefined ? c : false
}