How to pass variable by reference in javascript? Read data from ActiveX function which returns more than one value

问题

I have a ActiveX object which I want to use in the browser (javascript).
There is a function I want to call. Its prototype is:

function TOPOSFiscalPrinter.DirectIO(Command: Integer; var pData: Integer;
  var pString: WideString): Integer;

So, the function returns three values: result code, pData and pString;
In javascript the function does not update the variables pData and pString;

function test()
{
  var d=1, s="DIRECIO:";
  var code = opos.DirectIO(1024, d, s);

  alert(d); alert(s);
}

Variables d and s are not updated. They must be d=0 and s="ED123456";
How to read data from function which returns more than one value in javascript?

EDIT
Apparently, Javascript always passes parameters by value, never by reference.
Is there anything I can do to pass values by reference in Javascript, or I will have to change my design to only rely on parameters passed by value and on return values.

回答1:

Primitive types, primarily strings/numbers/booleans are passed by value for efficiency purposes. Objects such as functions, objects, arrays and the like are passed by reference. You can create an object and pass it, eg { d:1, s:'directo' } and then change the values because you're passing a reference.

回答2:

There is no support for output parameter in JavaScript. Pack what you want to return in an automation object, assign values to its properties and return it, or if your return value is already occupied, create a class that has properties you can assign to in your ActiveX and add a parameter whose type is the class. In your ActiveX you can use IDispatch/Ex to get/set the properties.

回答3:

Make a global variable or object. Or if you're worried about other funcs accessing and changing the variables then make a singleton. The other option is to return an object. Such as like this

function TOPOSFiscalPrinter.DirectIO(Command: Integer; var pData: Integer;
  var pString: WideString): Integer;

function TOPOSFiscalPrinter.DirectIO(Command, pData, pString){
    ....

    var pObj = {
        d: 0,
        s: '',
        code: ''
    }
    pObj.d = pDataAltertedValue;
    pObj.s = pStringAltertedValue;
    pObj.code = code;
    return pObj;
}

function test() 
{
    var d=1, s="DIRECIO:";
    var r = opos.DirectIO(1024, d, s);
    code = r.code;
    d = r.d;
    s = r.s;



    alert(d); alert(s);
}

回答4:

Primitives like int's or float's are always passed by value for performance reasons, but you can just wrap them into e.g. a Float32Array with just one element:

a = new Float32Array([123])
a[0]; // == 123
function ChangeA(a) {
    a[0] = 333;
}
ChangeA(a)
a[0]; // == 333

来源：https://stackoverflow.com/questions/1732557/how-to-pass-variable-by-reference-in-javascript-read-data-from-activex-function

标签

javascript

activex