I keep running into this obstacle every now and then. Consider this example:
> q = [] [] > for (var i = 0; i < 3; i++) q.push(function() { console.log(i); }); > q[0]() 3I wanted an array of three closures, each printing a different number to the console when called. Instead, each prints 3 (or, rather, whatever the value of the variable i happens to be).
I am not exactly sure about the reason, but presumably this happens because the i in each lambda refers to the variable i itself, not to its binding from the creation time of the function.
One solution is to enforce the bindings explicitly on each iteration, like this:
for (var i = 0; i < 3; i++) (function(v) { q.push(function() { console.log(v); }); })(i);Or use Underscore.js, which is what I actually do:
_([1,2,3]).each(function(i) { q.push(function() { console.log(i); }); });
