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Yash Singh
Function vs eval

Function vs eval

While working with eval to do some hacky workarounds in build configuration, I was curious about the difference between eval and Function. Here is what I found.


Quoting from tc39/proposal-hashbang:

Hashbang comments are only avilable at the start of a Script or Module parsing goal. Since eval uses Script it does support Hashbang comments. Since Function uses FunctionBody, it does not.

eval would execute the JavaScript code in the context of a module/script, while Function would execute it in the context of a function.

This means that Function would disallow hashbang comments, but allow the use of await (unless using top-level await, then available in Script also), and return.

For making use of generators and async functions, there are seperate constructors for them:

  • GeneratorFunction for generators
  • AsyncFunction for async functions
  • AsyncGeneratorFunction for both

According to MDN, the Function constructor also contains less security risks compared to eval.