Random Layers scale and opacity

function Random(max){
       return Math.round(Math.random()*(max-1))+1
    }
for (i=0;i<activeDocument.layers.length;i++){
        try{
        activeDocument.layers.opacity = Random(100)
        activeDocument.layers.resize(Random(100), Random(100))
        }catch(er){}
    }

Is the goal to apply a (different) random opacity and rescale to each layer?

I cleaned up the formatting of the code you pasted to make it easier to see what was going on:

#target photoshop
var aDoc = app.activeDocument;
var aSel = aDoc.selection;
var opMin = Number(prompt("min (0-1000%)", 0));
var opMax = Number(prompt("max (0-1000%)", 200));
if(opMin > opMax){
    temp = opMin;
    opMin = opMax;
    opMax = temp;
    }
if(opMin<0){
    opMIn = 0;
    }
if(opMax>1000){
    opMax = 1000;
    }
for(i=0; i<nSel; i++){
    var resScale = Math.floor(Math.random() * (opMax - opMin + 1)) + opMin;
    aSel.resize(resScale, resScale);
}

If my interpretation about what you are trying to do is correct, in line 4 you will want to use the aDoc.artLayers or aDoc.layerSets collections to grab the layers to loop through.

Another issue is in line 23 in which nSel is used (without having been declared). Presumably you would want to set this to the total number of layers you want to loop through.

The other confusing portion is line 24 in which opMin and opMax (the min and max for the desired opacity ranges?) are used to calculate the rescale factor. Should the rescaling depend on the opacity?

Hopefully this can get you started down the path to what you want to accomplish.