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I'm very new to javascript, but this topic seems to have attracted only scant forum attention. Given a number of simple functions:

function do_something(){...};
function do_somemore(){...};
function do_something_else(){...};

I was expecting to be able to assign these explicitly to cells in an (here 2D) array.

myMatrix[5][3] = do_something();
myMatrix[5][4] = do_somemore();
myMatrix[5][5] = do_something_else();

The reason I want to use such an approach are :

  1. simple to understand and maintain.
  2. eliminates potentially redundant anonymous function assignments in the array.

  3. any given function can be assigned to multiple array cells, for example:

    myMatrix[2][6] = do_somemore();
myMatrix[5][4] = do_somemore();
myMatrix[6][3] = do_somemore();

Unfortunately, calls such as the following (based on various forum examples, plus a little "suck it and see") are all failing.

x = myMatrix[5][4]do_somemore();         -> "missing ; before statement"
x = (myMatrix[5][4])do_somemore();       -> "missing ; before statement"
x = (myMatrix[5][4]do_somemore)();       -> "missing ) in parenthetical"
x = (myMatrix[5][4])(do_somemore());     -> "is not a function"
x = (myMatrix[5][4])()do_somemore();     -> "missing ; before statement"
x = myMatrix[5][4]()do_somemore();       -> "missing ; before statement"
x = myMatrix[5][4]();                    -> "is not a function"
x = (myMatrix[5][4])();                  -> "is not a function"

As I have no knowledge of javascript internals, I'd be glad of suggestions how to get the fuction calls firing.

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Many thanks to everyone who contributed insights. The code was working correctly within a couple of minutes assigning as follows: myMatrix[5][4] = do_somemore; ..and then calling using myMatrix[left][right](); The former I'd already tried, but the latter had escaped me :-) – Thug Apr 18 '11 at 15:48
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5 Answers

up vote 1 down vote

You should assign them like this:

myMatrix[5][3] = do_something;
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1  
Indeed. At the moment, the OP is calling the functions and assigning the returned values to the matrix. – Marcel Korpel Apr 18 '11 at 9:14
And the correct syntax to call such a function is x = myMatrix[5][3]();. Also notice that those parentheses are called ‘function call operator’. – Marcel Korpel Apr 18 '11 at 9:20
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up vote 0 down vote 
myMatrix[5][3] = do_something;

Your way would set the value to the RESULT of the function!

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up vote 0 down vote

I'm not entirely clear about what you are after, but:

First, before you can assign a value to an array, that array has to exist:

var myMatrix = [];
myMatrix[5] = [];
myMatrix[5][3] = … // Then you can assign something

Then, if you want to assign the return value of a function:

myMatrix[5][3] = do_something();

Or, if you want to assign the function itself:

myMatrix[5][3] = do_something;

… and then call it and assign its return value to x:

var x = myMatrix[5][3]();

… which is the same as var x = do_something() except that inside the function this will be myMatrix[5] instead of window.

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up vote 0 down vote 
myMatrix[5][3] = do_something; 
myMatrix[5][4] = do_somemore; 
myMatrix[5][5] = do_something_else; 


var x = myMatrix[5][3]();
var y = myMatrix[5][4]();
var z = myMatrix[5][5]();
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up vote 0 down vote

You are executing the functions immediately, so the value of e.g. myMatrix[5][5] will be the return value of that function. If you want myMatrix[5][5] to be a pointer to the function (and so be able to execute it later), use myMatrix[5][5] = do_something_else.

example:

var somearray = [[null,null]];
function test(){
  return 'tested';
}
somearray[0][0] = test;
alert(somearray[0][0]()); //=> 'tested'
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