Operator precedence with Javascript Ternary operator

javascript variable-assignment conditional-operator operator-precedence compound-assignment
Baijs picture Baijs · Nov 24, 2009 · Viewed 97.9k times · Source

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

Kobi picture Kobi · Nov 24, 2009 
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

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