Does actionscript have javascript’s gotchas?

Actionscript is a dialect of ECMAScript and therefore very close to javascript, but it really doesn’t feel it, especially when you’re following the usual advice to use static typing. I was curious if some of javascript’s peculiarities (like these and these) that trip up beginners come up in actionscript, too.

1. Floating point arithmetic - in javascript, 0.02 / 0.1 = 0.19999999999999998.

Actionscript: math is hard! Same result.

2. Semicolon insertion at line feed – in javascript, the following returns undefined instead of ‘aString’, which might seem odd at first glance.

Actionscript: if you add a type to the return value:

you get a compile error. But if you don’t add the return type, you get the same result. You might think that the Flashbuilder IDE would give a warning about unreachable code, but alas, it does not.

3. Attribute syntax can be confusing with arrays - setting an attribute on an array object can look like you’re adding an item to the array.

Actionscript: the same.

4. Setting variable scope – in javascript, ‘var x = y = 1′ will give x a local scope and y a global scope.

Actionscript: gives a compiler error that y is an undefined property.

5. ParseInt function - in javascript, parseInt(“000123″) returns 83.

Actionscript: returns 123! Maybe math isn’t so hard after all.