javascript - window.onload方法，如何调用多个函数

Question

编写一些 JavaScript，以便表单在字段已填写完毕后不会提交，如果用户尚未填写，则会弹出一条消息，提示“请填写姓名字段”或“请填写电子邮件字段”我正在为每个字段编写一个单独的函数(不知道这是否是正确的方法)，当我将每个函数添加到 window.onload 时，它只会弹出一条消息。任何建议都会很棒。

HTML

 <form id="frmContact" name="frmContact" method="post" action="thanks.htm">
    <fieldset id="quickSupport">
      <legend><strong>Quick Support</strong></legend>
      <p> If your request isn't urgent, drop us a quick line and we'll get back to you within 24 hours </p>
      <p>
        <label for="name">Name:</label>
        <input type="text" value="Your Name" name="name" id="name" tabindex="10" />
      </p>
      <p>
        <label for="email">Email:</label>
        <input type="text" value="Your Email" name="email" id="email" tabindex="20" />
      </p>
        <label for="comments">Comments </label>
        <br />
        <textarea name="comments" value="Message" id="comments" cols="45" rows="5" tabindex="60" onfocus="if(this.value==this.defaultValue)this.value='';" onblur="if(this.value=='')this.value=this.defaultValue;">Message</textarea>
      </p>
      <p>
        <input type="submit" name="submit" id="submit" value="Send" tabindex="70" />
      </p>
    </fieldset>
  </form>

   <p><span id="errorMessage"></span></p>
   <p><span id="errorMessage1"></span></p>

JavaScript

function prepareEventHandlers () {
document.getElementById("frmContact").addEventListener("submit", function(event) {

        // Show message
        if (document.getElementById("email").value == "Your Email") {
            document.getElementById("errorMessage").innerHTML = "Please provide at least an email address!";
            // to STOP the form from submitting
            return false;
        } else {
            // reset and allow the form to submit
            document.getElementById("errorMessage").innerHTML = "";
            return true;
        }

        event.preventDefault(); // Prevent form from submitting
    }
});
}

function prepareEventHandlersName () {
document.getElementById("frmContact").addEventListener("submit",         function(event) {

        // Show message
        if (document.getElementById("name").value == "Your Name") {
            document.getElementById("errorMessage1").innerHTML = "Please provide a name!";
            // to STOP the form from submitting
            return false;
        } else {
            // reset and allow the form to submit
            document.getElementById("errorMessage1").innerHTML = "";
            return true;
        }

        event.preventDefault(); // Prevent form from submitting
    }
});
}


function start() {
prepareEventHandlers();
prepareEventHandlersName();
}

window.onload = 开始;

Answer 1

您应该使用浏览器的内置验证属性。

<form id="frmContact" name="frmContact" method="post" action="thanks.htm">
    <fieldset id="quickSupport">
        <legend><strong>Quick Support</strong></legend>
        <p>If your request isn't urgent, drop us a quick line and we'll 
            get back to you within 24 hours</p>
        <p>
            <label for="name">Name:</label>
            <input type="text" value="Your Name" name="name" id="name" 
                tabindex="10" <em><strong>required</strong></em> />
        </p>
        <p>
            <label for="email">Email:</label>
            <input type="text" value="Your Email" name="email" id="email" 
                tabindex="20" <em><strong>required</strong></em> />
        </p>
        <label for="comments">Comments</label>
        <br />
        <textarea name="comments" value="Message" id="comments" cols="45" 
            rows="5" tabindex="60" 
            <em><strong>placeholder="PLACEHOLDER WHEN NO MESSAGE IS WRITTEN" required</strong></em>>Message</textarea>
        </p>
        <p>
            <input type="submit" name="submit" id="submit" value="Send" 
                tabindex="70" />
        </p>
    </fieldset>
</form>

当您尝试提交表单时，浏览器会自动以用户的语言为您显示友好的错误消息。无需 JavaScript。

<小时/>

您的代码失败的原因是，因为

document.getElementById("frmContact").onsubmit = ...

将覆盖您之前添加的任何 onsubmit 处理程序。

您需要使用.addEventListener() 相反，如果您想添加多个功能。

更正确的方法是创建一个执行所有检查的函数，并将其附加为处理程序一次。