Incorrect behaviour of (str obj) when obj has valueOf method

Question

Example

(str #js {"toString" (fn [] "hello") "valueOf" (fn [] 42)}) ; => "42"

The problem in the fact that ClojureScript uses concatenation to convert values to strings and that doesn't work well with objects which have valueOf() method overriden.

Example in js:

`
var obj = {

toString: function() { return 'hello'; },
valueOf: function() { return 42; }

};
console.log(String(obj)); => 'hello'
console.log(obj.toString()); => 'hello'
console.log('' + obj); => '42'
`

Potential solution might be to use String() function. Using toString() won't work as described in this issue: http://dev.clojure.org/jira/browse/CLJS-847

Answer 1

Comment made by: favila

Oops forgot tests.

Answer 2

_Comment made by: favila_

Update in CLJS-847: original reporter was not able to reproduce his original bug report in Safari 6.0.x running in BrowserStack. This may be because of BrowserStack, but it's the best we have.

Given how hard this bug is to reproduce, how few people it affects, and how significant the performance regression is, I still think we should go back to the simple {{(if (nil? x) "" (.toString x))}} implementation. However, you could also try the patch on this ticket (using a typeof switch), which at least (_handwaving_) *might* fix this bug in Safari 6.0.x and is a little faster than a simple .toString in Chrome and not much slower elsewhere. (The reason I think it might avoid this bug in Safari is that it avoids calling .toString on non-Objects.)

Answer 3

Comment made by: darwin

I wonder if you considered swapping str function at runtime during CLJS init phase.

Implement str function using plain .toString() call (original solution). And at startup check for Safari 6.0.x presence and optionally swap str for implementation wrapping .toString() call in a try-catch block silencing TypeError exceptions by falling back to Safari 6.0.x friendly .toString() alternative.

We would get correct semantics in all cases. And price would be just slower printing execution on Safari 6.0.x not on all systems.

Answer 4

Comment made by: mfikes

cljs-890.patch no longer applies

Answer 5

Reference: https://clojure.atlassian.net/browse/CLJS-890 (reported by nbeloglazov)