不喜欢代码高亮花花绿绿的样子，只设置了背景，没事再加个复制功能

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var codeblocks = document.getElementsByTagName("pre")
//循环每个pre代码块，并添加 复制代码

for (var i = 0; i < codeblocks.length; i++) {
//显示 复制代码 按钮
currentCode = codeblocks[i]
currentCode.style = "position: relative;"
var copy = document.createElement("div")
copy.style = "position: absolute;right: 4px;\
top: 4px;padding: 2px 8px;\
margin: 8px;cursor: pointer;\
z-index: 9999;"
copy.innerHTML = "复制"
currentCode.appendChild(copy)
//让所有 "复制"按钮 全部隐藏
copy.style.visibility = "hidden"
}

for (var i = 0; i < codeblocks.length; i++) {

!function (i) {
    //鼠标移到代码块，就显示按钮
    codeblocks[i].onmouseover = function () {
        codeblocks[i].childNodes[1].style.visibility = "visible"
    }

    //执行 复制代码 功能
    function copyArticle(event) {
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        //范围是 code，不包括刚才创建的div
        range.selectNode(codeblocks[i].childNodes[0]);

        const selection = window.getSelection();
        if (selection.rangeCount > 0) selection.removeAllRanges();
        selection.addRange(range);
        document.execCommand('copy');

        codeblocks[i].childNodes[1].innerHTML = "复制成功"
        setTimeout(function () {
            codeblocks[i].childNodes[1].innerHTML = "复制"
        }, 1000);
        //清除选择区
        if (selection.rangeCount > 0) selection.removeAllRanges(); 0
    }
    codeblocks[i].childNodes[1].addEventListener('click', copyArticle, false);

}(i);

!function (i) {
    //鼠标从代码块移开 则不显示复制代码按钮
    codeblocks[i].onmouseout = function () {
        codeblocks[i].childNodes[1].style.visibility = "hidden"
    }
}(i);
}
</script>

代码