JavaScript String.isWellFormed() method is used to check if the string contains a lone surrogate or not. A lone surrogate is a string that contains Unicode characters in the range 0xD800–0xDBFF and 0xDC00–0xDFFF. It returns trues if the lone surrogate is not present. If the string is not well-formed it will give an error if we use the encodeURI() method on it.
Syntax:
isWellFormed()
Parameters: It does not take any parameter
Return Value: A boolean, true if no lone surrogate is present, and false if the lone surrogate is present.
Example 1: This example uses the isWellFormed() method on strings.
Javascript
const str1 = "ab\uD800";const str2 = "new\uD800";const str3 = "hello";console.log(str1.isWellFormed());console.log(str2.isWellFormed());console.log(str3.isWellFormed()); |
Output:
false
false
true
Example 2: This example will perform the encodeURI function only on well-formed strings.
Javascript
const badFormed = "ab\uD800";const wellFormed = "hello";function checkFormation(str) { if(str.isWellFormed()){ console.log(encodeURI(str)) }}checkFormation(wellFormed);checkFormation(badFormed); |
Output:
hello
Supported Browsers:
- Chrome
- Edge
- Opera
- Safari
We have a complete list of Javascript string methods, to check those please go through this Javascript String reference article.
