I have seen usage like var f1=new Function(); but no more than that. Tried to search in Google regarding Function-class but nothing returned what I needed.
What is its significance?
Please suggest me how and when to use it. If possible give me some genuine link to study about it.
Best practice suggest you should never use a base type constructor functions. In a lot of case, use new with a base type will break the usage of typeof.
But, new Function() is valid JavaScript. Just not recommended, and not useful in most cases (var a= function() {} is equivalent).
Not that you can use the Function constructor as an eval call like so new Function('var a = 1; return a + a;'). But this can be dangerous, so use carefully.
eval capacity.
f1 after declaring it as: var f1=new Function(); i.e. I want to define it later than declaring it with Function constructor. Is there any way to do it?There isn't necessarily a beneficial reason to use new Function() since you could simply create a blank function like so:
var f1 = function () {
// my function code here;
};
// calling the function
f1();
Each one will have the prototypes of Function attached to it either way.
new Function() (also new Array(), etc) should typically be avoided since it has to eval.
new Function() won't.Technically, there really isn't a difference between these two bits of JavaScript (other answers have covered this):
var f1 = new Function();
and
var f1 = function () { };
What you can do, however, is use Function to check against the types of your variables:
var f1 = 'cat';
console.log(typeof(f1) === typeof(Function)); // false
var f2 = function () { return 'cat'; };
console.log(typeof(f2) === typeof(Function)); // true
Function objects created with the Function constructor are parsed when the function is created. This is less efficient than declaring a function and calling it within your code, because functions declared with the function statement are parsed with the rest of the code.
from MDN
