问题更改JavaScript中的边框颜色

Question

I am submitting a form, and it has validation to make sure my text box has a value. If false , the alert displays fine, however I can't get the border to change color. I can't seem to find out what I am doing wrong.

<script>
    function validate(){
        var dob = document.forms["ppm"]["dob"].value;
        if(dob == ""){
            document.getElementById("dob").style.border="red";
            alert("Error");
            return false;
        }
    }
</script>

<form onsubmit="return validate()" name="ppm" id="ppm" action="index.php" method="post">

<p>What is your DOB<br />
<input type="text" name="dob" id="dob" value="" />

<input type="submit" name="Continue" value="Continue"/>
</form>

Answer 1

You have to give the border the some width before it will be visible. You can use the individual border* properties for that:

document.getElementById("dob").style.borderColor ="red";
document.getElementById("dob").style.borderWidth ="2px";

Or, stick with border but supply a full border value (width, style, and color):

document.getElementById("dob").style.border = "2px solid red";

Here's a working example slightly modified from your original:

 function validate() { var dob = document.getElementById('dob').value; if (dob == null || dob == '') { document.getElementById("dob").style.border = "2px solid red"; alert("Error"); return false; } } 

 <p>What is your DOB <br /> <input type="text" name="dob" id="dob" value="" /> <input type="button" onclick="validate()" name="Continue" value="Continue" /> 

I'm tempted to rewrite your validate function into something like this:

function validate() {
  var dobEl = document.getElementById('dob'); // only get it once
  if (!(dobEl.value || '').length)) { // if null or empty
    dobEl.style.border = "2px solid red"; // set the style
    alert("Error");
    return false; // don't submit the form
  } else {
    // set the border back to normal
  }
  return true; // do submit the form
}

Answer 2

You are missing an end tag on your paragraph ( </p> ). You also need to set all parts of the border property when using style.border . Below is a working example.

  var isValid = function () { var dob = document.forms["ppm"]["dob"].value; if (dob === "") { document.getElementById("dob").style.border = "solid 1px red"; alert("Error"); return false; } return true; }; 

  <form onsubmit="return isValid();" name="ppm" id="ppm" action="index.php" method="post"> <p>What is your DOB</p> <br /> <input type="text" name="dob" id="dob" value="" /> <input type="submit" name="Continue" value="Continue" /> </form>