A safe integer is an integer that:

1. Can be exactly represented as an IEEE-754 double precision number, and
2. Whose IEEE-754 representation cannot be the result of rounding any other integer to fit the IEEE-754 representation

• Math.max() and Math.min() to find the closest safe value.
• Math.round() to convert to an integer.

const toSafeInteger = num =>
  Math.round(
    Math.max(Math.min(num, Number.MAX_SAFE_INTEGER), Number.MIN_SAFE_INTEGER)
  );

Examples:

let result1 = toSafeInteger('3.1');
let result2 = toSafeInteger('5.5');

console.log(result1); // 3
console.log(result2); // 6