how to replace numbers in body to persian numbers?

There is this findAndReplaceDOMText.js that may help you. It walks through all nodes in the document (as opposed to all elements) and replaces the text when the nodeType argument equals 3, which is TEXT_NODE.

This example will replace numbers in the whole page:

function walkNode(node) { 
    if (node.nodeType == 3) {
        // Do your replacement here
        node.data = node.data.replace(/\d/g,convert);
    }
        
    // Also replace text in child nodes
    for (var i = 0; i < node.childNodes.length; i++) {
        walkNode(node.childNodes[i]); 
    }
}
    
walkNode(document.getElementsByTagName('body')[0]);

function convert(a){
    return ['۰', '۱', '۲', '۳', '۴', '۵', '۶', '۷', '۸', '۹'][a];
}

See JavaScript String.replace documentation here.

You can use this method: (http://jsfiddle.net/A4NfG/1/)

persian={0:'۰',1:'۱',2:'۲',3:'۳',4:'۴',5:'۵',6:'۶',7:'۷',8:'۸',9:'۹'};
function traverse(el){
    if(el.nodeType==3){
        var list=el.data.match(/[0-9]/g);
        if(list!=null && list.length!=0){
            for(var i=0;i<list.length;i++)
                el.data=el.data.replace(list[i],persian[list[i]]);
        }
    }
    for(var i=0;i<el.childNodes.length;i++){
        traverse(el.childNodes[i]);
    }
}

If you want to select some elements by a selector, you can use this simple code (JsFiddle):

persian={0:'۰',1:'۱',2:'۲',3:'۳',4:'۴',5:'۵',6:'۶',7:'۷',8:'۸',9:'۹'};
$(".persian-digit").each(function(){
    for(var i=0;i<=9;i++) {
        var re = new RegExp(i,"g");
        $(this).html($(this).html().replace(re,persian[i]));
    }
});

Then for use it:

<span class="persian-digit">This span contains persian digits (0123456789),</span>
<span>and this one contains english digits (0123456789).</span>