Interval Comparison Doesn't Bomb In Js

Why doesn't interval comparison bomb in JavaScript? if(-1 < x < 1) { console.log('x: ', x) } Why are we allowed to do this without getting errors? Also it seems that: -1

Solution 1:

Because JavaScript allows implicit type coercion, in this case from boolean to number. The -1 < x results in a boolean, which is then implicitly coerced to a number (true = 1, false = 0) for the (result) < 1 part. So:

• When -1 < x is false, the second part is 0 < 1 which is true.

• When -1 < x is true, the second part is 1 < 1 which is false.

This is covered in the abstract relational comparison algorithm in the spec, and the various operations it links to.

-1 < x < -1is always false-2 < x < 2is always true

In the last 2 cases it seems it is just comparing the 2 ends of the expressions. How are those expressions evalued?

Using x = -1 and x = 1:

• If x = -1, then -1 < x is false, so the rest is 0 < -1, which is false.
• If x = 1, then -1 < 1 is true, so the rest is 1 < -1 which is false.
• If x = -1, then -2 < -1 is true, so the rest is 1 < -2, which is false.
• If x = 1, then -2 < 1 is true, so the rest is 1 < -2 which is false.

Solution 2:

I think that this happens because javascript implicitly considers true to have the value 1 and false to have the value 0.

When you do -1 < x < 1, what you're actually doing is (-1 < x) < 1, or true < 1 if x = 0 which is false.

However, if x=-2, (-1 < x < -1) will return true as false < 1 is true. Hope this helps.

You can read more about this here: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Comparison_Operators

Solution 3:

The reason is that JS interprets your expression.

if((-1 < x) < 1) {
  console.log('x: ', x)
}

Trying using braces...