In JavaScript
var x = (5 >= 9 >= 0);
console.log(x);
// returns true
What is happening in that statement and what is the reason for that output?
Asked
Active
Viewed 146 times
1
Peter Mortensen
- 30,738
- 21
- 105
- 131
Vishnu
- 11,614
- 6
- 51
- 90
-
This will create syntax error. Did you mean `var` instead of `boolean`? – Salman A Dec 26 '14 at 20:30
-
What do you think happens? – mplungjan Dec 26 '14 at 20:31
-
What did you expect instead of `true`? – Teemu Dec 26 '14 at 20:32
2 Answers
3
The Operator precedence and Associativity chart explains what is happening. The expression is evaluated in this order:
/* 1 */ x = (5 >= 9) >= 0;
/* 2 */ x = false >= 0;
/* 3 */ x = true;
Explanation:
>=is left associative the operator between 5 and 9 is evaluated first.>=uses abstract comparison which converts boolean to number i.e.falsebecomes 0 (ref).- The end result is
true.
Salman A
- 262,204
- 82
- 430
- 521
-
1
-
-
1
-
@adeneo—you're kidding? Because [*ToNumber(false)*](http://ecma-international.org/ecma-262/5.1/#sec-9.3) is zero. – RobG Dec 26 '14 at 21:32
-
@RobG - I'm not kidding, it's probably not very clear to everyone why `false >= 0` returns `true` as it's clearly not the same thing, or false being "more" than zero, it's because of the forced coercion to numbers on both sides, which is interesting. – adeneo Dec 26 '14 at 21:37
-
-
@adeneo—the greater–than and less–that operators use the [*abstract relation algorithm*](http://ecma-international.org/ecma-262/5.1/#sec-11.8.5), so there's a not–so–subtle hint that the comparison isn't strict. Maybe there's room for a strict relational comparison? ;-) – RobG Dec 26 '14 at 21:59
3
The true statement, is understood as different from zero... Consequently, false is equals zero...
The statement:
(5>=9>=0)
Turns into
(false >= 0)
Since 5 is lower than 9. Then, if false is equal zero the result is true
EDIT
As explained here (All falsey values in JavaScript), zero is among the falsy values in javascript...
