I don't know, but it seems that the problem comes from the way you use your ternary operators inside of the console.log, which might cause some issues. The basic logic is otherwise correct.

Code(100%):

function solve([x1, y1, x2, y2]) {

// let x1 = Number(input[0]);

// let y1 = Number(input[1]);

// let x2 = Number(input[2]);

// let y2 = Number(input[3]);

result(x1, y1, 0, 0);

result(x2, y2, 0, 0);

result(x1, y1, x2, y2);

// console.log(Number.isInteger(result(x1, y1))

// ? `{${x1}, ${y1}} to {0, 0} is valid`

// : `{${x1}, ${y1}} to {0, 0} is invalid`);

// console.log(Number.isInteger(result(x2, y2))

// ? `{${x2}, ${y2}} to {0, 0} is valid`

// : `{${x2}, ${y2}} to {0, 0} is invalid`);

// console.log(Number.isInteger((x1 - x2), (y1 - y2))

// ? `{${x1}, ${y1}} to {${x2}, ${y2}} is valid`

// : `{${x1}, ${y1}} to {${x2}, ${y2}} is invalid`);

function result(x1, y1, x2, y2) {

const distance = Math.sqrt((x1 - x2) ** 2 + (y1 - y2) ** 2);

const validString = Number.isInteger(distance) ? 'valid' : 'invalid';

console.log(`{${x1}, ${y1}} to {${x2}, ${y2}} is ${validString}`);

// return Math.sqrt((x1 - x2) ** 2 + (y1 - y2) ** 2);

}

}