Uncaught ReferenceError: Invalid left-hand side expression in postfix operation

Question

Why does my javascript throw the following exception

ReferenceError: Invalid left-hand side expression in postfix operation

function convertToEnd(p) {
        return ((((Number(p)-0)/100-0)*(1.5--0.5)-1.5)* -1);
}

Similar questions have been asked before here but as you can see from the various answers, the questions are very different (they usually result in an issue with a 3rd party, where as I have no third party), the only thing in common seems to be the exception string.

Answer 1

It's because of:

1.5--0.5

Change to:

1.5- -0.5

Alternatively a minifier will convert the whole calculation to:

return-1*(2*((Number(p)-0)/100-0)-1.5)