Iterating over arrays with for ... in causes unexpected behavior in some scenarios

[kumavis]

Iterating over arrays with for ... in breaks if additional functionality is added to Array.prototype.

// some polyfill or extension lib adds additional functionality
Array.prototype.first = function(){ return this[0] }

// your code tries to iterate with the for loop, causing undesirable behavior 
for( x in [1,2] ){ console.log(x) }
// (keys)
//=> 0
//=> 1
//=> first   <-- problematic

// forEach (and map) still work as expected
[1,2].forEach(function(x) { console.log(x) })
// (values)
//=> 1
//=> 2

[kumavis]

Compatibility tables for forEach and map
http://kangax.github.io/es5-compat-table/#Array.prototype.forEach
http://kangax.github.io/es5-compat-table/#Array.prototype.map

[3rd-Eden]

@kumavis Where am I iterating over an array with for in? If I'm doing that somewhere, it's definitely a bug.

edit:

Seems to be:

https://github.com/primus/primus/blob/master/primus.js#L485
https://github.com/primus/primus/blob/master/primus.js#L634

https://github.com/primus/primus/blob/master/spark.js#L87
https://github.com/primus/primus/blob/master/spark.js#L176

[kumavis]

@3rd-Eden PR incomming shortly

[kumavis]

@3rd-Eden you beat me to it ✌️

[3rd-Eden]

Fix released as 1.4.6