E0373: unexpected whitespace between '!' and '=='; '!' here treated as the TypeScript non-null assertion operator

While x! == y is legal TypeScript for a non-null assertion, it may be a typo for a strict inequality, as in x !== y:

let x = 17;
let y = 38;
if (x! == y) {
    alert('Not equal!');
}

To fix the warning, replace ! == with !==:

let x = 17;
let y = 38;
if (x !== y) {
  alert("Not equal!");
}

To suppress this warning, add parentheses around the non-null assertion:

let x = 17;
let y = 38;
if ((x!) == y) {
  alert("Not equal!");
}