variable assignment - Operator precedence with Javascript Ternary operator

Question

I cant seem to wrap my head around the first part of this code ( += ) in combination with the ternary operator.

h.className += h.className ? ' error' : 'error'

The way i think this code works is as following:

h.className = h.className + h.className ? ' error' : 'error'

But that isn't correct because that gives a error in my console.

So my question is how should i interpet this code correctly?

Answer 1

h.className = h.className + (h.className ? ' error' : 'error')

You want the operator to work for h.className, better be specific about it.
Of course, no harm should come from h.className += ' error', but that's another matter.

Also, note that + has precedence over the ternary operator: JavaScript Operator Precedence