Using Flash MX 2004 to open Flash 4 files

Flash 4 ActionScript had only one true data type: string. It used different types of operators in expressions to indicate whether the value should be treated as a string or as a number. In subsequent releases of Flash, you can use one set of operators on all data types.

When you use Flash 5 or later to open a file that was created in Flash 4, Flash automatically converts ActionScript expressions to make them compatible with the new syntax. You'll see the following data type and operator conversions in your ActionScript code:

• The = operator in Flash 4 was used for numeric equality. In Flash 5 and later, == is the equality operator and = is the assignment operator. Any = operators in Flash 4 files are automatically converted to ==.
• Flash automatically performs type conversions to ensure that operators behave as expected. Because of the introduction of multiple data types, the following operators have new meanings:

  +, ==, !=, <>, <, >, >=, <=

  In Flash 4 ActionScript, these operators were always numeric operators. In Flash 5 and later, they behave differently depending on the data types of the operands. To prevent any semantic differences in imported files, the Number() function is inserted around all operands to these operators. (Constant numbers are already obvious numbers, so they are not enclosed in Number()).

• In Flash 4, the escape sequence \n generated a carriage return character (ASCII 13). In Flash 5 and later, to comply with the ECMA-262 standard, \n generates a line-feed character (ASCII 10). An \n sequence in Flash 4 FLA files is automatically converted to \r.
• The & operator in Flash 4 was used for string addition. In Flash 5 and later, & is the bitwise AND operator. The string addition operator is now called add. Any & operators in Flash 4 files are automatically converted to add operators.
• Many functions in Flash 4 did not require closing parentheses, for example, Get Timer, Set Variable, Stop, and Play. To create consistent syntax, the getTimer function and all actions now require closing parentheses. These parentheses are automatically added during the conversion.
• In Flash 5 and later, when the getProperty function is executed on a movie clip that doesn't exist, it returns the value undefined, not 0. The statement undefined == 0 is false in ActionScript after Flash 4 (in Flash 4, undefined == 1). In Flash 5 and later, solve this problem when converting Flash 4 files by introducing Number() functions in equality comparisons. In the following example, Number() forces undefined to be converted to 0 so the comparison will succeed:

  getProperty("clip", _width) == 0 
  Number(getProperty("clip", _width)) == Number(0)
  

Note: If you used any Flash 5 or later keywords as variable names in your Flash 4 ActionScript, the syntax returns an error when you compile it in Flash MX 2004. To solve this problem, rename your variables in all locations. See Keywords and Naming a variable.