JavaScript的（0 ==“”）=== true如何与ECMA-262类型转换规则一致？

Question

I've already seen several questions explaining why 0 == "" is true in JavaScript , but i have a bit deeper question.

So the answer to why is 0 == "" is true in JavaScript is that string "" gets converted to number, zero-length string is converted to zero number, but how this agrees with [9.3.1 paragraph of ECMA-262](http://www.ecma-international.org/ecma-262/5.1/#sec-9.3.1) which says that string should be parsed using given formal grammar and if it fails, then such string is converted to NaN . When i looked on this spec i thought that "" is not a string numeric literal and it should be parsed as NaN and NaN is not equal to 0.0 .

So why above speculation isn't correct and 0 == "" is actually true ?

Thanks in advance.

Answer 1

The grammar allows for StringNumericLiteral to be empty:

StringNumericLiteral :::
StrWhiteSpace _opt
StrWhiteSpace _opt StrNumericLiteral StrWhiteSpace _opt

A few lines down, it says:

A StringNumericLiteral that is empty or contains only white space is converted to +0 .

and:

The MV of StringNumericLiteral ::: [empty] is 0.

So I'm afraid you simply didn't fully read the standard passage you're looking at. :)