Javascript dynamic function

Question

I have associative arrays within an array that is created and passed as an argument within an object method like so:

myObject.method([
    {
        id: "mystring",
        myfun: function(g) {
                   return 'Value: ' + g.value + g.rows[0]['value'];
                   },
        a: "mysecondstring"
    },
        id: "mystring_a",
        myfun: function(g) {
                   return 'Value: ' + g.value + g.rows[0]['value'];
                   },
        a: "mysecondstring_a" 
    }]);

I have plenty of instances of this throughout my code and this works fine. The value of g is not declared beforehand. Now I want to change the myfun: function(g)... at run time, which requires that I declare my associative array before calling myObject.method(). Here is what I have tried:

myfun: new Function("g", "return 'Value: ' + g.value + " + my_dynamic_variable)

no good, then tried:

var fn = new Function("g", "return 'Value: ' + g.value + " + my_dynamic_variable)

with

myfun: fn(g)

and this

myfun: function(g) { return fn }

and this

var fn = function(g) { return eval('Value: ' + g.value + my_dynamic_variable) }

with

myfun: fn

Everything I have tried turns up null for g once the myfun code is executed. I'm guessing that variable g must be bound within the scope of myObject, and that I cannot define it outside of the myObject scope, but I am not certain.

Anyone know of a way to do this? Am I missing the mark here? Thanks!

This definitely looks like an XY problem. What's the real world use case? Maybe you need to think about a different data structure... — elclanrs
– elclanrs, Commented Aug 14, 2014 at 22:59
If you assign a function to the key its argument week be evaluated when it's called, e.g., you can reassign it to a new function the same way you assign it the first time. g is evaluated when the function is executed, it's a parameter. — Dave Newton
– Dave Newton, Commented Aug 14, 2014 at 23:04
Right, you just need to store that function, and pass a reference to it, var f = function(g){return 'Value: '+ g.value + g.rows[0].value}, then myfun: f — elclanrs
– elclanrs, Commented Aug 14, 2014 at 23:05
Now why didn't I think of that? Thanks everyone...geez...the answer seems so simple now you pointed it out... :) @elclanrs - it works! Much appreciated. If you post your comment as an answer, I will accept it. — ionalchemist
– ionalchemist, Commented Aug 14, 2014 at 23:23

elclanrs · Accepted Answer · 2014-08-14 23:44:40Z

1

You can store that function in a variable:

var f = function(g){return 'Value: '+ g.value + g.rows[0].value}

Then pass a reference to it:

myfun: f

answered Aug 14, 2014 at 23:44

elclanrs

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