String.prototype.isWellFormed()

isWellFormed()

const strings = [
  // 
  "ab\uD800",
  "ab\uD800c",
  // 
  "\uDFFFab",
  "c\uDFFFab",
  // 
  "abc",
  "ab\uD83D\uDE04c",
];

for (const str of strings) {
  console.log(str.isWellFormed());
}
// Logs:
// false
// false
// false
// false
// true
// true

const illFormed = "https://example.com/search?q=\uD800";

try {
  encodeURI(illFormed);
} catch (e) {
  console.log(e); // URIError: URI malformed
}

if (illFormed.isWellFormed()) {
  console.log(encodeURI(illFormed));
} else {
  console.warn(""); // 
}