DOM基础教程之使用DOM设置文本框

1.控制用户输入的字符个数

对于单行文本框和密码输入框，可以利用maxlength属性控制用户输入的字符个数。
对于多行文本，maxlength为自定义属性，其值最多输入的字符的个数，在onkeypress事件发生时则调运返回LessThan()函数返回值，函数如下

<textarea name="comments" id="comments" cols="40" rows="4" maxlength="50" onekeypress ="return LessThan(this);"></textarea>
详细代码

代码如下:

<script language="javascript">
function LessThan(oTextArea){
    //返回文本框字符个数是否符号要求的boolean值
    return oTextArea.value.length < oTextArea.getAttribute("maxlength");
}
</script>
<form method="post" name="myForm1" action="addInfo.aspx">
<p><label for="name">请输入您的姓名:</label>
<input type="text" name="name" id="name" class="txt" value="姓名" maxlength="10"></p>
<p><label for="comments">我要留言:</label><br>
<textarea name="comments" id="comments" cols="40" rows="4" maxlength="50" onkeypress="return LessThan(this);"></textarea></p>
<p><input type="submit" name="btnSubmit" id="btnSubmit" value="Submit" class="btn">
<input type="reset" name="btnReset" id="btnReset" value="Reset" class="btn"></p>
</form>

2.设置鼠标经过自动选择文本

首先是鼠标经过时自动聚焦 onmouseover = "this.focus"

其次是 onfocus = "this.select()"
代码实例:

代码如下:

<form method="post" name="form1" id="form1" action="addInfo.aspx">
<input type="text" name="name" id="name" class="txt" value="姓名" onmouseover="this.focus()" onfocus="this.select()">
</form>

对于多个代码实例，可以使用以下代码进行聚焦

代码如下:

<script type="text/javascript">
            function myFocus() {
                this.focus();
            }
            function mySelect() {
                this.select();
            }
            window.onload = function() {
                var oForm = document.forms["myForm1"];
                oForm.name.onmouseover = myFocus;
                oForm.name.onfocus = mySelect;
            }
        </script>
            <form method="post" name="myForm1" action="addInfo.aspx">
                <p>
                    <label for="name">请输入您的姓名:</label>
                    <input type="text" name="name" id="name" class="txt" value="姓名">
                </p>
                <p>
                    <label for="passwd">请输入您的密码:</label>
                    <input type="password" name="passwd" id="passwd" class="txt">
                </p>
                <p>
                    <input type="submit" name="btnSubmit" id="btnSubmit" value="Submit" class="btn">
                    <input type="reset" name="btnReset" id="btnReset" value="Reset" class="btn">
                </p>
            </form>