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 // for-of works on strings and String objects.

 load(libdir + "string.js");

 function test(s, expectedCodePoints) {

     var copy = '';

     var codepoints = 0;

     var singleHighSurrogate = false;

     for (var v of s) {

         assertEq(typeof v, 'string');

         assertEq(v.length, isSurrogatePair(v) ? 2 : 1);

         assertEq(false, singleHighSurrogate && isLowSurrogate(v));

         copy += v;

         codepoints += 1;

         singleHighSurrogate = !isSurrogatePair(v) && isHighSurrogate(v);

     }

     assertEq(copy, String(s));

     assertEq(codepoints, expectedCodePoints);

 }

 test('', 0);

 test('abc', 3);

 test('a \0 \ufffe \ufeff', 7);

 // Non-BMP characters are generally passed to JS in UTF-16, as surrogate pairs.

 // ES6 requires that such pairs be treated as a single code point in for-of.

 test('\ud808\udf45', 1);

 // Also test invalid surrogate pairs:

 // (1) High surrogate not followed by low surrogate

 test('\ud808', 1);

 test('\ud808\u0000', 2);

 // (2) Low surrogate not preceded by high surrogate

 test('\udf45', 1);

 test('\u0000\udf45', 2);

 // (3) Low surrogate followed by high surrogate

 test('\udf45\ud808', 2);

 test(new String(''), 0);

 test(new String('abc'), 3);

 test(new String('a \0 \ufffe \ufeff'), 7);

 test(new String('\ud808\udf45'), 1);

 test(new String('\ud808'), 1);

 test(new String('\ud808\u0000'), 2);

 test(new String('\udf45'), 1);

 test(new String('\u0000\udf45'), 2);

 test(new String('\udf45\ud808'), 2);