對(duì)于單行文本框和密碼輸入框，可以利用maxlength屬性控制用戶輸入的字符個(gè)數(shù)。
對(duì)于多行文本，maxlength為自定義屬性，其值最多輸入的字符的個(gè)數(shù)，在onkeypress事件發(fā)生時(shí)則調(diào)運(yùn)返回LessThan()函數(shù)返回值，函數(shù)如下

<textarea name="comments" id="comments" cols="40" rows="4" maxlength="50" onekeypress ="return LessThan(this);"></textarea>
詳細(xì)代碼

復(fù)制代碼代碼如下:

<script language="javascript">

function LessThan(oTextArea){

    //返回文本框字符個(gè)數(shù)是否符號(hào)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">請(qǐng)輸入您的姓名:</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.設(shè)置鼠標(biāo)經(jīng)過(guò)自動(dòng)選擇文本

首先是鼠標(biāo)經(jīng)過(guò)時(shí)自動(dòng)聚焦 onmouseover = "this.focus"

其次是 onfocus = "this.select()"
代碼實(shí)例:

復(fù)制代碼代碼如下:

<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>

對(duì)于多個(gè)代碼實(shí)例，可以使用以下代碼進(jìn)行聚焦

復(fù)制代碼代碼如下:

<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">請(qǐng)輸入您的姓名:</label>

                    <input type="text" name="name" id="name" class="txt" value="姓名">

                </p>

                <p>

                    <label for="passwd">請(qǐng)輸入您的密碼:</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>