Why does (0 < 5 < 3) return true?

Why does (0 < 5 < 3) return true?

I was playing around in jsfiddle.net and I’m curious as to why this returns true?
if(0 < 5 < 3) { alert("True"); } So does this: if(0 < 5 < 2) { alert("True"); } But this doesn't: if(0 < 5 < 1) { alert("True"); } Is this quirk ever useful?

Solutions/Answers:

Solution 1:

Order of operations causes (0 < 5 < 3) to be interpreted in javascript as ((0 < 5) < 3) which produces (true < 3) and true is counted as 1, causing it to return true.

This is also why (0 < 5 < 1) returns false, (0 < 5) returns true, which is interpreted as 1, resulting in (1 < 1).

Solution 2:

My guess is because 0 < 5 is true, and true < 3 gets cast to 1 < 3 which is true.

Solution 3:

probably because true is assumed as 1 so

0 < 5 < 3  -->  true < 3 -->  1 < 3  --> true

Solution 4:

Because true < 3, because true == 1

Solution 5:

As to your question whether this quirk is ever useful: I suppose there could be some case where it would useful (if condensed code is what you are after), but relying on it will (most likely) severely reduce the understandability of your code.

It’s kind of like using post/pre increment/decrement as a part of bigger expressions. Can you determine what this code’s result is at a glance?

int x = 5;
int result = ++x + x++ + --x;

Note: with this code, you can sometimes even get different results depending on the language and compiler.

It’s a good idea to make life easy for yourself and the next guy who will read your code. Clearly write out what you actually want to have happen rather then relying on side effects like the implicit conversion of booleans.

Solution 6:

The answer to the second part of the question, “is this quirk ever useful?” is perhaps no, as noted by a previous answer, if it is indeed a quirk of the language (Javascript) that true is cast to 1, but that the programmer does not in general view 1 and true (and 0 and false) as the same thing.

If however you have a mental model of 1 being true and 0 being false, then it leads to all sorts of nice boolean techniques that are extremely useful, powerful, and direct. For example, you could increment a counter directly with the result of A > 100, which would increment the counter if A is greater than 100. This technique might be viewed as a quirk or a trick in Java, but in an array or functional language may be idiomatic.

A classic example in the array language APL would be to count the number of items in an array that are (say) greater than 100:

+/A>100

Where if A is the 5 item array 107 22 256 110 3 then:

A>100

yields the 5 item boolean array:

1 0 1 1 0

and summing this boolean result:

+/1 0 1 1 0

yields the final answer:

3

This question is a perfect example of where this technique would be very useful, especially if the problem is generalized to determine if n out of m boolean values are true.

Check if at least two out of three booleans are true