PDFJS has a member variable numPages, so you'd just iterate through them. BUT it's important to remember that getting a page in pdf.js is asynchronous, so the order wouldn't be guaranteed. So you'd need to chain them. You could do something along these lines:

var currPage = 1; //Pages are 1-based not 0-based

var numPages = 0;

var thePDF = null;



//This is where you start

PDFJS.getDocument(url).then(function(pdf) {



        //Set PDFJS global object (so we can easily access in our page functions

        thePDF = pdf;



        //How many pages it has

        numPages = pdf.numPages;



        //Start with first page

        pdf.getPage( 1 ).then( handlePages );

});







function handlePages(page)

{

    //This gives us the page's dimensions at full scale

    var viewport = page.getViewport( 1 );



    //We'll create a canvas for each page to draw it on

    var canvas = document.createElement( canvas );

    canvas.style.display = block;

    var context = canvas.getContext('2d');

    canvas.height = viewport.height;

    canvas.width = viewport.width;



    //Draw it on the canvas

    page.render({canvasContext: context, viewport: viewport});



    //Add it to the web page

    document.body.appendChild( canvas );



    //Move to next page

    currPage++;

    if ( thePDF !== null && currPage <= numPages )

    {

        thePDF.getPage( currPage ).then( handlePages );

    }

}