Understanding the ActionScript Language > Using Flash MX ActionScript with older versions of Flash > Using Flash MX to open Flash 4 files |  |

Using Flash MX 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 Flash 5 and Flash MX, 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 Flash MX, `==` 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 Flash MX, 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 Flash MX, 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 Flash MX, `&` 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 Flash MX, 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. Flash fixes 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 Flash MX keywords as variable names in your Flash 4 ActionScript, the syntax returns an error in Flash MX. To fix this, rename your variables in all locations. See Keywords.