我建议你使用未充分利用的 TreeWalker DOM API，如下:

I suggest you use the under-utilized TreeWalker DOM API, as follows:

var walk = document.createTreeWalker(document, NodeFilter.SHOW_TEXT, null, false),
    n;

while(n = walk.nextNode()) {
    n.nodeValue = n.nodeValue.replace(/foo/g, 'bar');
}

NodeFilter.SHOW_TEXT 告诉 TreeWalker 您只对文本节点感兴趣.请参阅 https://developer.mozilla.org/en/docs/Web/API/树行者了解更多信息.

The NodeFilter.SHOW_TEXT tells TreeWalker you only are interested in text nodes. See https://developer.mozilla.org/en/docs/Web/API/TreeWalker for more information.

但是你想用更复杂的 DOM 结构替换文本，涉及到 em 元素，所以我们需要做更多的工作:

But you want to replace the text with a more complex DOM structure, involving the em element, so we have to do a bit more work:

function emphasize(regexp) {
    var walk = document.createTreeWalker(document, NodeFilter.SHOW_TEXT, null, false),
        n, span;

    while (n = walk.nextNode()) {
        newVal = n.nodeValue.replace(regexp, function(match) { 
            return "<em>" + match + "</em>";
        });

        if (newVal !== n.nodeValue) {
            span = document.createElement('span');
            span.innerHTML = newVal;
            n.parentNode.replaceChild(span, n);
        }
    }
}

Nodewalker 可能不会很高兴将其当前节点从其下方替换掉.这需要进行一些测试和可能的调整.

It could be Nodewalker will not be too happy about having its current node being replaced out from under it. That would require a bit of testing and possible tweaking.