Placing library item into page

Question

This script for placing library item into page and applying object style to the item. In line 16, script shows that "assets" property does not support. Please resolve this.
if (app.documents.length==0){
    alert("Please open the Document");
    exit();
if (app.libraries.length==0){
    alert("Please open the Library");
    exit();
app.findTextPreferences=app.changeTextPreferences=null;
app.findTextPreferences.appliedParagraphStyle="MN";
var myfound=app.activeDocument.findText();
alert(myfound.length);
for(i=0; i<myfound.length; i++){
var mylib=app.libraries.assets.itemByName("Box").placeAsset(myfound[i].insertionPoints[0]);
var mymove=myfound[i].move(LocationOptions.atBeginning, mylib.insertionPoints[0])
mylib.appliedObjectStyle="MN_Obj";

Answer 1

To make that work, you have to address an open library (line 16).
app.libraries describes the collection of all open libraries, not a distinct one.
If only one library is open you could address the one with its index:
app.libraries[0]
If you already know the name of the library or better, the exact path of the library, you can:
1. Make sure to open it
2. Call it by its name
Let's assume you know the name and you know that the asset you want to place is stored inside, you could do it this way:
app.libraries.itemByName("TheNameOfTheLibrary").assets.itemByName("Box").placeAsset(
/*Wherever you want*/
Now, what will this line return?
A library object? Hardly. So be cautious with using a variable name like "mylib".
According to documentation it is returning an Array, and we can assume, that in this array is the object that is placed out of the library. Your asset stored in the library which goes by the name of "Box". Whatever that is.
If you want to find out, you can use the following, more descriptive variable: "myPlacedAsset". That sounds more neutral.
var myPlacedAsset = app.libraries.itemByName("TheNameOfTheLibrary").assets.itemByName("Box").placeAsset(
/*Wherever you want*/
Using the ESTK (ExtendScript Toolkit) together with $.writeln() can write the true nature of the placed asset to your JavaScript Console:
$.writeln(myPlacedAsset.constructor.name);
is informing you what kind of object "myPlacedAsset" really is. If indeed it is an Array, you could look for its length. If its length is "1", you get to the "heart" of your placed object by:
$.writeln(myPlacedAsset[0].constructor.name);
Or by that more inquisitory question:
$.writeln(myPlacedAsset[0].getElements()[0].constructor.name);
If your array is of a greater length, you have to loop through this array and question every single object!
Before testing, exchange my comment "/*Wherever you want*/" with the code you like to use: Obviously the first insertion point of your found text. Hold on! This will backfire to you, because every time you place one instance of the asset you will add a character to your found text and shift the original insertionPoint. Better loop from back to forth or do the search from back to forth.
Adobe InDesign CS6 (8.0) Object Model JS: Text
Please, try that and report back…
(Isn't noone reading the documentation these days?)
Indesign JavaScript Help
Adobe InDesign CS6 (8.0) Object Model JS: Table of Contents, Libraries Suite
Adobe InDesign CS6 (8.0) Object Model JS: Library
Adobe InDesign CS6 (8.0) Object Model JS: Asset
Adobe InDesign CS6 (8.0) Object Model JS: Asset
Uwe