Enables faster program execution.
- +| -
/fast is on by default. /fast or /fast+ causes the compiler to generate an output file that is speed-optimized, however, if this option is used certain language features from previous versions will not be supported. Specifying /fast-, on the other hand, will provide for backward language compatibility, but the compiler will produce an output file that is not optimized for speed.
When /fast is in effect,
All variables must be declared.
Functions become constants and you cannot assign to them or redefine them.
Predefined properties of built-in objects are marked DontEnum, DontDelete, ReadOnly.
Properties on the built-in objects may not be expanded, other than the Global object (which is also the global scope).
The arguments variable is not available within function calls.
Assignments to read-only variables, fields, or methods generate errors.
The /fast- compilation mode is provided to help developers build standalone executables from legacy JScript code. When developing new executables or libraries, use the /fast+ compilation mode. This ensures better performance and better compatibility with other assemblies.
The /fast- compilation mode enables the use of language features from previous versions not available in /fast+ mode. Misuse of these features can result in a program with weaker security. For more information, see Security Considerations for JScript.
Create an output file that is speed-optimized at the expense of full backward language compatibility: