The isWellFormed()
method of String
values returns a boolean indicating whether this string contains any lone surrogates.
The isWellFormed()
method of String
values returns a boolean indicating whether this string contains any lone surrogates.
isWellFormed()
None.
Returns true
if this string does not contain any lone surrogates, false
otherwise.
Strings in JavaScript are UTF-16 encoded. UTF-16 encoding has the concept of surrogate pairs, which is introduced in detail in the UTF-16 characters, Unicode code points, and grapheme clusters section.
isWellFormed()
allows you to test whether a string is well-formed (i.e. does not contain any lone surrogates). Compared to a custom implementation, isWellFormed()
is more efficient, as engines can directly access the internal representation of strings. If you need to convert a string to a well-formed string, use the toWellFormed()
method. isWellFormed()
allows you to handle ill-formed strings differently from well-formed strings, such as throwing an error or marking it as invalid.
const strings = [ // Lone leading surrogate "ab\uD800", "ab\uD800c", // Lone trailing surrogate "\uDFFFab", "c\uDFFFab", // Well-formed "abc", "ab\uD83D\uDE04c", ]; for (const str of strings) { console.log(str.isWellFormed()); } // Logs: // false // false // false // false // true // true
encodeURI
throws an error if the string passed is not well-formed. This can be avoided by using isWellFormed()
to test the string before passing it to encodeURI()
.
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("Ill-formed strings encountered."); // Ill-formed strings encountered. }
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Chrome | Edge | Firefox | Opera | Safari | Chrome Android | Firefox for Android | Opera Android | Safari on IOS | Samsung Internet | WebView Android | Deno | Node.js | ||
isWellFormed |
111 | 111 | 119 | 97 | 16.4 | 111 | 119 | 75 | 16.4 | 22.0 | 111 | 1.32 | 20.0.0 |
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https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/isWellFormed