Pages And Margins

This script fits a page to a text frame

    var doc = app.documents.add();
    var page = doc.pages.item(0);
    var tf = page.textFrames.add({
        geometricBounds:[12.7,12.7,100,210],
        contents: "Hi God, it's me - Jesus."
        });
       
        tf.paragraphs.item(0).pointSize = 42;
        tf.fit(FitOptions.FRAME_TO_CONTENT);
        
       
    
        doc.documentPreferences.pageWidth = tf.geometricBounds[3] + 12.7;
        doc.documentPreferences.pageHeight = tf.geometricBounds[2] + 12.7;
        
        var new_pw = doc.documentPreferences.pageWidth;
        var new_ph = doc.documentPreferences.pageHeight;
        
        tf.geometricBounds = [12.7,12.7,new_ph - 12.7,new_pw - 12.7];   

The next script shows how many fun you can have with pageItems

    var doc;
    if(app.documents.length > 0){
        doc = app.activeDocument;
        }else{
        doc = app.documents.add();     
    }
    
    /**
     *  A document has always a page 
     *  so we don't need to create one  
     */
    var page = doc.pages.item(0);
    // could also be 
    // var page = doc.pages.lastItem();
    // now lets do some stuff on that page
    
    var gb = [10,10,50,50]; // some bounds
        page.ovals.add({geometricBounds:gb}); // add an oval
        // increase x values
        gb[1]+=10;
        gb[3]+=10;
        page.rectangles.add({geometricBounds:gb}); // add an rectangle
        // increase x values again
        gb[1]+=10;
        gb[3]+=10;
        page.textFrames.add({geometricBounds:gb}); // add an textFrame
    
        // a page has not only ovals and so on
        // it also has pageItems
        // loop them
    for(var i = 0; i < page.pageItems.length; i++){
            // now get the y value
        var y = page.pageItems[i].geometricBounds[1];
            // and move them
            page.pageItems[i].move([ 10 + (10*i),y]);    
        }
    
        // now duplicate the page
        page.duplicate();

###margins
Margins are the grid for your layout.

    var doc = app.documents.add({
    
        });
    var page = doc.pages.item(0);
    page.marginPreferences.properties = {
        top : 30,
        left: 30,
        right: 30,
        bottom:30
        };

Have a look at the tons of different options and properties you can set. This script also creates a new layer and connects several textFrames.

    /**
     *  Lets build a doc
     */
    main();
    function main(){
        
    // add a doc
    var doc = app.documents.add(); 
    // lets store some data in an object for better handling
    meta = {
            "pw":200,
            "ph":200,
            "top":20,
            "left":20,
            "bottom":20,
            "right":20,
            "gutter":5,
            "textColumnCount":5
            };
    
    // have a look at the build function below
    doc_build(doc, true,false,meta);
    
    // now lets make something with those pages
    var count = 0; // counter
    var range = 10; // until
    var frames = []; // to store the textFrames
    // now loop it
    while(count < range){
        // the first page is always there
        // so we have to check if we are at index 0
        var page;
        if(count != 0 ){
        page = doc.pages.add(); // if not add a page
        }else{
        page = doc.pages[0]; // we are at index 0 take the existing page
        }
        // apply a master spread
        page.appliedMaster = doc.masterSpreads.item(0);
        // add a textFrame and push it into an array
        // for better handling
        frames.push(page.textFrames.add());
        // now get the margins from the page
        // the get bounds function is part of the
        // Scripting Tutorial Hello World from the SDK
        frames[count].geometricBounds = myGetBounds(doc, page);
        // once again we have to check if we are at index 0
        // because the textFrame 0 cant have a previous text frame
        // if we are not at 0 connect the actual textFrame with the previous  
        if(count != 0){
            frames[count].previousTextFrame = frames[count-1];
            }
        // now we change the gutter on every second text frame
        // just for the fun of it.
        // get the gutter from the page 
        // and give the textFrame the same margins
        if((count%2) == 0){
            frames[count].textFramePreferences.properties = {
            textColumnCount : page.marginPreferences.columnCount/2,
            textColumnGutter : page.marginPreferences.columnGutter
            };
         }
         //increment the count for the next loop
        count++;
        }
    // add some placeholder text
    frames[0].contents = TextFrameContents.placeholderText;
    // The End
    return 0;
    };
    
    
    /**
     *  Lets build a document
     *  with lots of preferences
     */
    function doc_build(doc, makeColumns,facingPages,meta){
        doc.layers.item(0).name = "the standard layer";    
        doc.layers.add({name:"a new layer"});
            if(facingPages){
            doc.documentPreferences.facingPages = true;
        }else{
            doc.documentPreferences.facingPages = false;
        }
    
        // set some view parameters
        doc.viewPreferences.properties = {
            horizontalMeasurementUnits: MeasurementUnits.MILLIMETERS,
            verticalMeasurementUnits:MeasurementUnits.MILLIMETERS
        };
        // set the page size and bleed box
        doc.documentPreferences.properties = {
            pageWidth : meta.pw,
            pageHeight : meta.ph,
            documentBleedBottomOffset : 3,
            documentBleedTopOffset : 3,
            documentBleedInsideOrLeftOffset : 3,
            documentBleedOutsideOrRightOffset : 3
        };
        
        // the baseline settings
        doc.gridPreferences.properties = {
         baselineStart : meta.top
        }
        
        // how big are the steps
        doc.gridPreferences.baselineDivision = "15pt";
    
    // lets create some master spreads
    var master_spread1 = doc.masterSpreads.item(0).pages.item(0);// edit the master spreads
     
        master_spread1.marginPreferences.properties = {
            right:meta.right,
            top:meta.top ,
            left:meta.left ,
            bottom:meta.bottom + 10,
            columnGutter:meta.gutter*2,
        };  
    
    var master_spread2 = doc.masterSpreads.item(0).pages.item(1);//edit the other master spread
    
        master_spread2.marginPreferences.properties = {
            right:meta.right,
            top:meta.top,
            left:meta.left,
            bottom:meta.bottom,
            columnGutter:meta.gutter
        };  
    
        if(makeColumns){
            master_spread1.marginPreferences.columnCount = meta.textColumnCount*2;
            master_spread2.marginPreferences.columnCount = meta.textColumnCount;
        }
    
    
    }// end make doc
    
    // part of
    //ImprovedHelloWorld.jsx from InDesign scripting SDK
    //An InDesign CS6 JavaScript
    
    function myGetBounds(myDocument, myPage){
        var myPageWidth = myDocument.documentPreferences.pageWidth;
        var myPageHeight = myDocument.documentPreferences.pageHeight
        if(myPage.side == PageSideOptions.leftHand){
            var myX2 = myPage.marginPreferences.left;
            var myX1 = myPage.marginPreferences.right;
        }
        else{
            var myX1 = myPage.marginPreferences.left;
            var myX2 = myPage.marginPreferences.right;
        }
        var myY1 = myPage.marginPreferences.top;
        var myX2 = myPageWidth - myX2;
        var myY2 = myPageHeight - myPage.marginPreferences.bottom;
        return [myY1, myX1, myY2, myX2];
    }