It's quite common to see codes using new Function, instead of simply Function. I want to understand why, what exactly the new operator is doing here.
What's the difference between these two?
var y = new Function("a", "alert(a)") var x = Function("a", "alert(a)") From the docs:
The
Functionconstructor creates a newFunctionobject. In JavaScript every function is actually aFunctionobject....
Invoking the
Functionconstructor as a function (without using the new operator) has the same effect as invoking it as a constructor.
Since functions are actually objects in Javascript, it is possible to call them both via standard invocation syntax and the new operator (which instantiates a new object of type Function in this case).
What that last line I quoted from the docs is saying is that doing Function() is identical to calling new Function().
There is no difference.
The difference is that when you invoke the function with a new keyword it creates a new 'this' empty object for your function and you can set properties on that inside your function. Also the return value from your new-ly called function will be this if you do not return something else.
With no new keyword there's no new empty 'this' object so if you are using that inside it will error out.
You might not be using this at all in your function so you may see no differences at all.
p.s.: One problem might be that if you are using this and you invoke without the new kw. the this will be the global this inside the fn. - and in a browser environment that will be the window object... so you will be setting props on that instead of on a plain new empty obj.
Function. It's defined to behave the same either way. "WhenFunctionis called as a function rather than as a constructor, it creates and initializes a new Function object."StringandNumberpretty much, ...Booleannew(iethisis the global object, then it self invokes as a constructor)