toWellFormed < String < JavaScript

The toWellFormed() of a String returns a string where all lone surrogates of the string are replaced with the Unicode replacement character U+FFFD.

    
    const loneLeadingSurrogate = "ab\uD800".toWellFormed();
    console.log(loneLeadingSurrogate);
    // "ab�"

    const loneLeadingSurrogate1 = "ab\uD800c".toWellFormed();
    console.log(loneLeadingSurrogate1);
    // "ab�c"

    const loneTrailingSurrogate = "\uDFFFab".toWellFormed();
    console.log(loneTrailingSurrogate);
    // "�ab"

    const wellFormed = "ab\uD83D\uDE04c".toWellFormed();
    console.log(wellFormed);
    // "ab😄c"