Search code examples
javascriptcomparison-operators

What happens when doing triple comparison? (Javascript)

First up: I know this is not how one should do a comparison, this is merely a question of interest. Let's say you do this comparison:

var x = 0;
if(1 < x < 3) {
  console.log("true");
} else {
  console.log("false");
}

What is happening inside that if-statement so that the output is "true"? Is there some implicite logical comparison happening. And how do I find out?

Solution

  • The comparison takes place from left to right so 1 < x < 3 will evaluate as

    1 < x first which is false, given that x is 0. Here the next comparison will be,

    false < 3 which will be true because there will be implicit type conversion of false to numeric representation, which is 0. So, the expression evaluates to 0 < 3 which is true.

    Hence, when you do true < 3 or false < 3 then this boolean value will be implicitly converted to 0 as false and 1 as true.