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Are these two functions doing the same thing behind the scenes? (in single statement functions)
var evaluate = function(string) { return eval('(' + string + ')'); } var func = function(string) { return (new Function( 'return (' + string + ')' )()); } console.log(evaluate('2 + 1')); console.log(func('2 + 1')); 
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Again, eval() is much slower than Function() . However, eval() is also slower than the alternatives since it has to invoke the JavaScript interpreter, while many other constructs are optimized by modern JS engines. Additionally, modern JavaScript interpreters convert JavaScript to machine code.
alternatives to eval() or Function() for common use-cases. The difference between eval() and Function() is that the source string passed to Function() is parsed as function body, not as a script. There are a few nuances — for example, you can use return statements in a function body but not in a script.
The Eval function evaluates the string expression and returns its value. For example, Eval("1 + 1") returns 2. If you pass to the Eval function a string that contains the name of a function, the Eval function returns the return value of the function.
eval() is evil if running on the server using input submitted by a client that was not created by the developer or that was not sanitized by the developer. eval() is not evil if running on the client, even if using unsanitized input crafted by the client.
No, they are not the same.
eval() evaluates a string as a JavaScript expression within the current execution scope and can access local variables.new Function() parses the JavaScript code stored in a string into a function object, which can then be called. It cannot access local variables because the code runs in a separate scope.Consider this code:
function test1() { var a = 11; eval('(a = 22)'); alert(a); // alerts 22 } If new Function('return (a = 22);')() were used, the local variable a would retain its value. Nevertheless, some JavaScript programmers such as Douglas Crockford believe that neither should be used unless absolutely necessary, and evaling/using the Function constructor on untrusted data is insecure and unwise.
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new Function creates a function that can be reused. eval just executes the given string and returns the result of the last statement. Your question is misguided as you attempted to create a wrapper function that uses Function to emulate an eval.
Is it true that they share some code behind the curtains? Yes, very likely. Exactly the same code? No, certainly.
For fun, here's my own imperfect implementation using eval to create a function. Hope it sheds some light into the difference!
function makeFunction() { var params = []; for (var i = 0; i < arguments.length - 1; i++) { params.push(arguments[i]); } var code = arguments[arguments.length - 1]; // Creates the anonymous function to be returned // The following line doesn't work in IE // return eval('(function (' + params.join(',')+ '){' + code + '})'); // This does though return eval('[function (' + params.join(',')+ '){' + code + '}][0]'); } The biggest difference between this and new Function is that Function is not lexically scoped. So it wouldn't have access to closure variables and mine would.
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