isFinite()

function div(x) {
  if (isFinite(1000 / x)) {
    return "Number is NOT Infinity.";
  }
  return "Number is Infinity!";
}

console.log(div(0));
// Expected output: "Number is Infinity!""

console.log(div(1));
// Expected output: "Number is NOT Infinity."

isFinite(testValue)

isFinite(Infinity); // false
isFinite(NaN); // false
isFinite(-Infinity); // false

isFinite(0); // true
isFinite(2e64); // true，在更强壮的 Number.isFinite(null) 中将会得到 false

isFinite("0"); // true，在更强壮的 Number.isFinite('0') 中将会得到 false