Open a console window and type

1 < 2 < 3

and the output will be true.

So far so good, lets try another example. Now type

3 > 2 > 1 we get false. whoops!

Turns out 1 < 2 < 3 returning true was a complete accident and something else was going behind the scenes.

Evaluating a comparision expression

To understand whats going on,lets understand how a comparision is evaluated

Here is the link if someone wants to go through the spec. 262.ecma-international.org/12.0/#sec-abstra..

While evaluating a comparision operation, say x > y, both x and y are first coerced to numeric values

For example

let x = 3, y = 2;

x > y          //outputs true

in the above block since both x and y are already numeric, they are returned as it is and a numerical comparision takes place

The Answer

Now that we have a basic idea of how a comparision expression is evaluated, lets get back to our earlier code

let x = 3, y = 2, z = 1

 3 > 2 > 1 

// this is evaluated left to right so, the expression is evaluated as 

(3 > 2) > 1

//which becomes

true > 1

Since the comparision is broken down into two operations, the result of first operation is compared to the right most operand, which in our case becomes,

true > 1

// first coerce true to a numeric value

+true     //outputs 1

//the expression after coercion becomes

1 > 1   // finally outputs false

Thanks for reading!