PS scripting in JS. How to acquire the Content Layer of a Frame Layer's?

[PDD.PDD]

So when I make a scriptto automate, I need to trim an image in the frame and resize it to its original ratio and resize to fit the frame. 

Currently I am using the 'activeLayer' property to access that layer after execute an action of 'replace content in frame', I wonder if there's way to select the content layer directly without changing the active layer of the document.

[c.pfaffenbichler]

Does »Replace Contents« not work in your set-up? 

Could you provide sample files or at least screenshots with the pertinent Panels (Toolbar, Layers, Options Bar, Properties, …) visible? 

[Stephen Marsh]

Groups, Artboards and Frame layers are all variants of layerSets. To access a layer without making it active, you can use it's index number.

[Stephen Marsh]

Further to my previous post.

Assuming that the frame layer is active and that it has content, selecting the top frame layer's content by index number:

app.activeDocument.activeLayer = app.activeDocument.activeLayer.layers[0];

.

 Or using the first layerSet index number in the collection (you obviously need to know which layerSet index number to target, as opposed to the entire layers collection):

app.activeDocument.activeLayer = app.activeDocument.layerSets[0].layers[0];

Or just using the layers absolute position in the stack (not isolating by layerSet), such as the very back layer index:

app.activeDocument.activeLayer = app.activeDocument.layers[app.activeDocument.layers.length - 1].layers[0];

I haven't tried replacing content, hopefully the same principle applies.