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javascriptecmascript-5

Converting eval() to new Function()

Given an arbitrary eval(), is there a way to convert it to use new Function(), without breaking compatibility with any input (except for the change in scope)?

The only issue I can think of is that eval allows multiple statements, and returns the result of the last one, without having to add an explicit return. I cannot think of a way to emulate this with new Function():

let code = '4; 5'
> eval(code);
5
> new Function(code)();
undefined
> new Function('return ' + code)();
4
> new Function('return (' + code + ')')();
SyntaxError: Unexpected token ;

Is there something I am missing or is eval() incompatible with new Function() in this case?

Solution

  • No, this is indeed impossible with Function(). The eval function is the only JavaScript feature that takes statement results into account.