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var defaultButton = document.getElementById('<%= lnkSearch.ClientID %>');
if (defaultButton && typeof(defaultButton.click) == 'undefined') {
    defaultButton.click = function() {
        alert('function fired');
        var result = true;
        if (defaultButton.click) result = defaultButton.onclick();
        if (typeof(result) == 'undefined' || result) {
            eval(defaultButton.getAttribute('href'));
        }
    };
    alert(typeof(defaultButton.click) != 'undefined');
}

if (defaultButton && typeof(defaultButton.click) != "undefined") { ... }

<div id="abc_pnlSearchPanel" language="javascript" onkeypress="javascript:return WebForm_FireDefaultButton(event, 'abc_lnkSearch')">
    <div class="searchPanel">
        <span class="searchText">
            Type in stuff to search:
        </span>
        <span style="float: left;">
    		<input name="abc:txtSearch" type="text" id="abc_txtSearch" style="width:312px;" />
    	</span>
        <a onclick="this.blur();" id="abc_lnkSearch" class="ButtonLayout" href="javascript:__doPostBack('abc$lnkSearch','')"><span>Search</span></a>
        <div style="clear: both"></div>
    </div>
</div>

<body onLoad="DefaultButtonFix()">