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b.querySelector('b').textContent=p.title; b.querySelector('small').textContent=p.hint;
b.onclick=function(){show(i);};
nav.appendChild(b); buttons.push(b);
});
function show(i){
i=(i+pages.length)%pages.length; if(i===cur)return; cur=i;
buttons.forEach(function(b,k){b.setAttribute('aria-current',k===i?'true':'false');});
frame.srcdoc=pages[i].src;
try{location.hash='#'+(i+1);}catch(e){}
document.title=(i+1)+'. '+pages[i].title+' · 一年级数学图形动画';
frame.addEventListener('load',function once(){frame.removeEventListener('load',once);try{frame.contentWindow.focus();}catch(e){}});
}
document.getElementById('prev').onclick=function(){show(cur-1);};
document.getElementById('next').onclick=function(){show(cur+1);};
document.getElementById('fs').onclick=function(){
var d=document; if(d.fullscreenElement){d.exitFullscreen();} else {d.documentElement.requestFullscreen&&d.documentElement.requestFullscreen();}
};
window.addEventListener('message',function(e){
if(e.data&&e.data.nav==='PageDown')show(cur+1); else if(e.data&&e.data.nav==='PageUp')show(cur-1);
});
document.addEventListener('keydown',function(e){
if(e.key==='PageDown'){e.preventDefault();show(cur+1);} else if(e.key==='PageUp'){e.preventDefault();show(cur-1);}
});
var h=parseInt((location.hash||'').replace('#',''),10);
show(isNaN(h)?0:clampIdx(h-1));
function clampIdx(i){return Math.max(0,Math.min(pages.length-1,i));}
})();