How to call anonymus function from string

Question

I have string containg anonymus function definition, but how i can call this. Lets say function is like so:

var fn_str = "function(){ alert('called'); }";

Tried eval, but got an error that function must have a name.

eval(fn_str).apply(this); // SyntaxError: function statement requires a name

You call `eval` with `a` while the function string is in `fn_str`. that won't work this way... — gdoron, Mar 09 '12 at 08:33
Sorry, i used a in firebug console for shortness but forgot to change this, good eye though — Kristian, Mar 09 '12 at 08:35

score 8 · Accepted Answer · edited May 23 '17 at 12:15

8

You can use Immediately Invoked Function Expression:

var fn_str = "function(){ alert('called'); }";
eval('(' + fn_str +')();');

Another way is to use to a Function object (If you have the function body string):

var func = new Function("alert('called')");
func.apply(this);

edited May 23 '17 at 12:15

Community

answered Mar 09 '12 at 08:28

gdoron

1

Already figured out, but thanks! Accept/+1 for quick response :) – Kristian Mar 09 '12 at 08:30

score 3 · Answer 2 · answered Mar 09 '12 at 08:39

3

You can create functions from strings using the Function constructor:

var fn = new Function("arg1", "alert('called ' + arg1);");
fn.apply(this)

answered Mar 09 '12 at 08:39

steveukx

score 1 · Answer 3 · answered Mar 09 '12 at 08:27

1

Found the solution: Put function in parentheses

var a = "(function(){ alert('called'); })";
eval(a).apply(this);

answered Mar 09 '12 at 08:27

Kristian

1

You don't need to write use `apply` you can use *Immediately Invoked Function Expressions** as I answered. – gdoron Mar 09 '12 at 08:29
I know that syntax, but i cant pass an object as a parameter that way(without parsing an object to string). Or can i? – Kristian Mar 09 '12 at 08:34
What did you mean in that comment, I didn't understand it. What do you need? – gdoron Mar 09 '12 at 09:06
Sample code: `var fn = "function(object, cb) { /* Do something with the object */ }"; var obj = { param: value, param2: value2 }; eval('('+fn')').apply(this, [obj]);` – Kristian Mar 09 '12 at 09:10
Can you get the function body? without the `function(object, cb){ ` part – gdoron Mar 09 '12 at 09:13
I could if i'll parse the string and strip `function(){` and `}` from it, but i alrealy solved my case. Thanks anyways – Kristian Mar 09 '12 at 09:16

3 Answers3