Javascript instance with variable method

Question

Is there a way to make an instance string / method variable? For example

function drag(type){
    //replace type in string below
    fabric.type.prototype.controls.moveObject = new fabric.Control({
        x: -0.5,
        y: -0.5,
        actionHandler: fabric.controlsUtils.dragHandler,
        actionName: 'drag',
        cursorStyle:'pointer',
        render:renderIcon(dragIcon),
        cornerSize: 25
    });
}

Hope somebody has the answer for me :)