如何使输入字段不区分大小写

我已经制作了一个数组，我要找出记录，当我要找到大写单词的记录时，它是ok的，但是当我要找到小写字母的记录时，它不是找到记录。以下是我编写的脚本:

if (document.getElementById('drop_down_list_1').value == "Genetic") {
    if (document.getElementById('search_input').value == "") {
        alert("Please Enter a charactor / word..");
    } else {
        var con = document.getElementById('first_div');
        var con2 = document.getElementById('first_div2');
        var char = document.getElementById('search_input').value;
        var str = '';
        var j = 0;
        var ad = ['GLARIFIDE Deadlines 2012 - 2013 Nov', 'REPRODUCTIVE VACCINES — REPRODUCTIVE CLAIMS', 'M', 'M', 'R'];
        var len = ad.length;
        //char.toLowerCase().indexOf(ad) != -1;
        var break_line = '<br>';
        for (j = 0; j < len; j++) {
            var str = ad[j];
            var n = str.indexOf(char);
            if (n == 0)
                con.innerHTML += '<table id="results" style="margin-top: -3px;"><tr><td>' + str + '</td><td id="td1"><a href="javascript:presenter.command(''viewPdf'',{''path'': ''/images/pdf/Dairy/' + j + '.pdf''});"><img src="images/view.png" style="margin-left:250px;"></a><img src="images/email.png"></td></tr></table>' + break_line;
            break_line = '<br>';
        }
    }
}