Why is 0 == "" in JavaScript?

[gappodi]

Why is
0 == "" in JavaScript

Since "A" + 0 != "A" + ""

thank you.
Gap

[Evertjan.]

wrote on 21 mrt 2008 in comp.lang.javascript:

Why is
0 == "" in JavaScript

because

var result = 0 == "";

is not the same as

var result = 0 === "";

==========

With:

var result = 0 == "";

both being near equivalent to false,
and
var result = false == false;

results in true.
--
Evertjan.
The Netherlands.
(Please change the x'es to dots in my emailaddress)

[Stevo]

ga*****@gmail.com wrote:

Why is
0 == "" in JavaScript

Since "A" + 0 != "A" + ""

Well, "A"+0 is "A0".

As for 0 == "", that's all done to automatic type conversions and the
fact that javascript considers false, 0, "", undefined all as false, and
the rest as true. So 0 is false and "" is false, therefore 0==""

[Douglas Crockford]

ga*****@gmail.com wrote:

Why is
0 == "" in JavaScript

Since "A" + 0 != "A" + ""

Mistakes were made.

[Rick Merrill]

Thomas 'PointedEars' Lahn wrote:

ga*****@gmail.com wrote:

>Why is
0 == "" in JavaScript

Steps of evaluation (cf. ECMAScript Ed. 3 Final, sections 11.9.1 to 11.9.3):

0 == ""
+0 == +0
true

>Since "A" + 0 != "A" + ""

"A" + 0 != "A" + ""
!("A" + +0 == "A" + "")
!("A" + "0" == "A" + "")
!("A0" == "A")
!(false)
true
PointedEars

i think i see your answer to the OP is correct,
but how do you explain the apparent contradiction
0 == ""
AND
0 == "0"

?

[Thomas 'PointedEars' Lahn]

Rick Merrill wrote:

Thomas 'PointedEars' Lahn wrote:

>ga*****@gmail.com wrote:

>>Why is
0 == "" in JavaScript

Steps of evaluation (cf. ECMAScript Ed. 3 Final, sections 11.9.1 to 11.9.3):

0 == ""
+0 == +0
true

>>Since "A" + 0 != "A" + ""

"A" + 0 != "A" + ""
!("A" + +0 == "A" + "")
!("A" + "0" == "A" + "")
!("A0" == "A")
!(false)
true
[...]

Please trim your quotes, do not quote signatures unless referring directly
to them.

i think i see your answer to the OP is correct,
but how do you explain the apparent contradiction
0 == ""
AND
0 == "0"

What is perceived as a contradiction by the OP and you here is ignoring that
string concatenation also involves type conversion.
PointedEars
--
var bugRiddenCrashPronePieceOfJunk = (
navigator.userAgent.indexOf('MSIE 5') != -1
&& navigator.userAgent.indexOf('Mac') != -1
) // Plone, register_function.js:16

[Joost Diepenmaat]

Rick Merrill <ri***********@gmail.comwrites:

i think i see your answer to the OP is correct,
but how do you explain the apparent contradiction
0 == ""
AND
0 == "0"

That's not a contradiction, that's just type conversion.

See section 11.8.5 of the emacascript 262 specs:

The Abstract Equality Comparison Algorithm

The comparison x == y, where x and y are values, produces true or
false. Such a comparison is performed as follows:

1. If Type(x) is different from Type(y), go to step 14.

[ snip ]

14. If x is null and y is undefined, return true.
15. If x is undefined and y is null, return true.
16. If Type(x) is Number and Type(y) is String,
return the result of the comparison x == ToNumber(y).
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^
[ snip ]

ToNumber("0") and ToNumber("") both evaluate to 0.
--
Joost Diepenmaat | blog: http://joost.zeekat.nl/ | work: http://zeekat.nl/

[Thomas 'PointedEars' Lahn]

Joost Diepenmaat wrote:

See section 11.8.5 of the emacascript 262 specs:

It is ECMA-262 or ECMAScript, not both. Otherwise you are correct.
PointedEars
--
var bugRiddenCrashPronePieceOfJunk = (
navigator.userAgent.indexOf('MSIE 5') != -1
&& navigator.userAgent.indexOf('Mac') != -1
) // Plone, register_function.js:16