关于函数的调用疑问

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<title>无标题文档</title>
<style type="text/css">
    #div1{width:200px;height:30px;background-color:red;}
    #div2{width:150px; height:20px;background-color:gray;margin-top:10px;display:none;}
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<script type="text/javascript">
    window.onload = function () {
        var div1 = document.getElementById("div1");
        var div2 = document.getElementById("div2");
        var timer = null;
        function show() {
            div2.style.display = "block";
            clearTimeout(timer);
        }
        function hide() {
            timer = setTimeout(function () { div2.style.display = "none"; }, 300);
        }
        div1.onmouseover = show;
        div1.onmouseout = hide;
        div2.onmouseover = show;
        div2.onmouseout = hide;
    }
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<div id="div1"></div>
<div id="div2"></div>
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        div1.onmouseover = show;
        div1.onmouseout = hide;
        div2.onmouseover = show;
        div2.onmouseout = hide;为啥我要是写成div1.onmouseover = show();
                                              div1.onmouseout = hide();
                                              div2.onmouseover = show();
                                              div2.onmouseout = hide();就不行呢？函数的调用不得加上后面的括号吗？求解答

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1回答

慕无忌8876879

加上括号，你的方法就执行了，但是不会赋值给你的div1.onmouseover了，当出发你的div1.onmouseover的时候就不会调用show了

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