Can some tell me why the following code returns true in JavaScript?
console.log(true > null); //returns true
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14Yes because null is a falsy expression (then false) and comparison operator will convert it to a number (then true = 1 and false = 0).Adriano Repetti– Adriano Repetti2012-07-23 14:41:30 +00:00Commented Jul 23, 2012 at 14:41
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2@Adriano post it as answer is just that!elclanrs– elclanrs2012-07-23 14:42:11 +00:00Commented Jul 23, 2012 at 14:42
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stackoverflow.com/questions/801032/null-object-in-javascriptxkeshav– xkeshav2012-07-23 14:42:20 +00:00Commented Jul 23, 2012 at 14:42
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@elclanrs I'm lazy to write a complete answer with references to JavaScript standard (for who is interested just start from section 11.8.2).Adriano Repetti– Adriano Repetti2012-07-23 14:46:17 +00:00Commented Jul 23, 2012 at 14:46
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7 Answers
null is like false in this case, wich is 0 as a number. true is 1 as a number.
1 is bigger (>) than 0.
1 Comment
GrantVS
Thanks for the answer. I was wondering why is null === 0 false? Then I realised it needs to be coerced. So for those who need absolute proof, try + null === 0 which evaluates to true proving that indeed null is coerced to 0. Just thought this might help others.
They are converted to numbers, null gives 0 and true gives 1
http://ecma-international.org/ecma-262/5.1/#sec-11.8.5
If it is not the case that both Type(px) is String and Type(py) is String, then
- Let nx be the result of calling ToNumber(px). Because px and py are primitive values evaluation order is not important.
- Let ny be the result of calling ToNumber(py).
Number(null) //0
Number(true) //1
Comments
May be because true = 1 where null = 0
Comments
JavaScript does a lot of type coercion in the background and a lot of the results you'll find aren't useful (see http://wtfjs.com/).
In this case, true which is coerced as 1 is greater than null which is coerced to 0. Since 1 is greater than 0 the result is true.
If one of the operands is Boolean, the Boolean operand is converted to 1 if it is true and +0 if it is false.
From the MDN.
Comments
What's happening behind is that the relational operators ( > in this case) perform type coercion before doing the comparison. When doing the ToPrimitive, true gets coerced to a 1, and null to a 0.
You can check details here of how the operators actually work here
Comments
The code is incorrect, you need to do:
console.log(true > typeof null);
Comments
The compare operator ">" forces both it's left and right side to be converted to numbers. Number(true) is 1, Number(null) is 0, so what is in the paranthesis is taken as "1>0", which is always true in result.
