eval(fn) and eval(arrowFn) returns different value

Question

As per the Mozilla docs in order to execute a function using eval it must be wrapped inside ( ) i.e. if you don\'t use them then it treate

Answer 1

The documentation says nothing on function execution. The functions won't be executed, unless they are executed explicitly like (() => {})().

The quote

eval as a string defining function requires "(" and ")" as prefix and suffix

refers to interpreting the string as function expression rather than function declaration.

// will throw SyntaxError
// because function declaration requires a name
typeof eval('function (){}'); 

typeof eval('function a(){}') === 'undefined';
typeof eval('(function a(){})') === 'function';
typeof eval('null, function a(){}') === 'function';
typeof eval('()=>{}') === 'function';

Arrow function is always an expression, it doesn't need auxiliary constructions like comma or parentheses to interpret is an expression, here is the difference.