What is "" in JavaScript really? -

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this 1 says false, meaning "" number:

alert(isnan(""));

this 1 says nan, meaning "" not number , cannot converted:

alert(parsefloat(""));

i expecting second code convert "" 0 since "" number when tested in isnan wrong! getting crazy or missed something?

parsefloat tries parse number string isnan converts argument number before checking it:

number("") //0 http://ecma-international.org/ecma-262/5.1/#sec-9.3.1 parsefloat("") //nan http://ecma-international.org/ecma-262/5.1/#sec-15.1.2.3

apparently "broken" or "confusing", specs:

a reliable way ecmascript code test if value x nan expression of form x !== x. result true if , if x nan.

0 !== 0 // false nan !== nan //true  function isexactlynan(x) {     return x !== x; }

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