renderPage.js

function renderPage(pageNumToRender = 1) {
    isPageRendering = true; 
    document.getElementById('current_page_num').textContent = pageNumToRender;
    // use getPage method
    
    pdf
      .getPage(pageNumToRender)
      .then( page => {
        const viewport = page.getViewport({scale :1});
        canvas.height = viewport.height;
        canvas.width = viewport.width;  
        let renderCtx = {canvasContext ,viewport};
        
        page
          .render(renderCtx)
          .promise
          .then(()=> {
            isPageRendering = false;
            // this is to check if there is next page to be rendered in the queue
            if(pageRenderingQueue !== null) { 
                renderPage(pageRenderingQueue);
                pageRenderingQueue = null; 
            }
        });
    }); 
}