New in Flash 7
The way Flash handles some variables when publishing a swf to Flash 7 is used in a movie has changed a little. These fairly minor, though important changes are the no. 1 cause of complications when porting Flash MX and earlier versions of movies to Flash MX 04. Understand that you do NOT have to convert your older movies for them to work in the new Flash player. Even though they are published to a lower format, the new player will treat them accordingly as based on the version of the swf. If they ain't broke, don't fix them. These changes are only for when publishing to the new Flash 7 format and applies to both ActionScript 1.0 and ActionScript 2.0 in that format. When working in ActionScript 2.0, chances are you are targeting the new player, so these need to be understood. Here's the run-down:

1. Case sensitivity
In a Flash 7 swf, all variables and keywords are case sensitive. This means that myvariable is not the same as myVariable. If used (as variables) Flash will interpret each to have their own separate values. This also means that attachmovie() will no longer attach a movie from your library onto the screen. The correct command is attachMovie() with a capital M.

If you've been a sloppy coder in the past, or just not keeping correct capitalization (that doesn't necessarily make you "sloppy"), this may be a problem. Now you'll have to be sure to maintain consistency with capitalization. With Flash objects and methods, color coding can help. With your own variables, you'll just have to keep to your guns and be consistent.

2. Undefined variable values have changed
When you use a variable that has not been previously defined somewhere in your script, Flash needs to assume a certain default value for that variable. This value is based on the context of where its first used; is it being used as a number? as a string? With Flash 6, this definition is 0 if used as a number and an empty string (""), even though technically the variable is still considered undefined. When using Flash 7, these default values have changed. Now, if an undefined variable is used as a number, a NaN is given; if as a string, the string "undefined" is given.

var name, job;

name = "George";

trace(name+" works for "+job);

// F6: "George works for "

// F7: "George works for undefined"

var value;

value++;

trace(value);

// F6: 1

// F7: NaN

3. String boolean value has changed
Now with Flash 7 strings, as long as they aren't empty, they have a boolean value of true. This means that when they are seen in a true/false situation, as long as the string has some value, it is seen as being true. This includes strings like "0". In Flash 6, strings are first converted to a number and then evaluated to being if that number was non-zero and false if not (i.e. if 0). Flash 6 will interpret "0" as being false; Flash 7 will not as it is not empty. To Flash 6 any non-numeric string is false. To Flash 7, as long as it has length, no matter if its numeric or not, it's true. Look at the following chart for examples.

4. Removed array lengthening with string indexing
Though you may have never known it or even made us of it, with Flash 6, you could extend the length of an array if you tried assigning a value to an index of that array outside of its length if using a string that was not a specific array index but could be parsed into one (i.e. a string that when used with parseInt would result in a number). The string "5tuna", for example, is not fully numeric so cannot specify a specific index of an array. However, when parsed into a number, that value becomes 5. If you tried to assign the index "5tuna" of an array with a length less than 6 in Flash 6, that array's length would then reach out to be 6 to account for the supposed index (even though, oddly enough, no actual value would be assigned to it). Now, when publishing your swf to Flash 7, that is not possible. Using strictly numeric strings, however, is still acceptable and will continue to work fine.

myList = new Array(2);

trace(myList.length); // 2

trace(parseInt("5tuna")); // 5

myList["5tuna"] = "anything";

 

trace(myList.length); // F6: 6, F7: 2

trace(myList[5]); // undefined

Now, with that out of the way, we can start focusing in more on Actionscript 2.0.

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