gistfile1.js

function MySymbol(input){
    this.doc = app.activeDocument;
    this.mySymbolIndex = input || 0; 
    this.mySymbolItem = this.hasSymbolIndex() ? this.doc.symbolItems[this.mySymbolIndex] : false;
}

MySymbol.prototype.hasSymbolIndex = function() {
    return this.mySymbolIndex <= this.doc.symbolItems.length - 1;
};

MySymbol.prototype.getWidth = function() {
    return this.mySymbolItem ? Math.round(this.mySymbolItem.width) : 0;
};

MySymbol.prototype.getHeight = function() {
    return this.mySymbolItem ? Math.round(this.mySymbolItem.height) : 0;
};

// returns width and height as an array
MySymbol.prototype.getWidthHeight = function() { 
    var widthAndHeight = [];
    widthAndHeight.push(this.getWidth());
    widthAndHeight.push(this.getHeight());
    return widthAndHeight;
}

var firstSymbol = new MySymbol(0);