CODEWITHSUNDEEP
javascript
CTViking
CTViking

Reputation: 97

Error: Cannot read property 'value' of null

I am extremely new to javascript and so I apologize in advance for any problems with the way I am asking my quesion. I am trying to post data and have a warning pop up if all fields are not filled out. And one of the fields is a radio type. Here is a link to a jsfiddle with my script http://jsfiddle.net/J2yWQ/64/

Here is what I have at the moment

function emailWarning() {
    var check = document.getElementById("check");
    check.className = 'show';
}

function validateEmail(xem) {
    var re = /\S+@\S+\.\S+/;
    return re.test(xem);
}

function postData() {
        email = 'email'+document.getElementById('email').value;
    var tt = validateEmail(email);
    if (tt == true) {
        xmlhttp.open('POST', 'payment.php', true);
        xmlhttp.setRequestHeader('Content-type', 'application/x-www-form-urlencoded');
        xmlhttp.send(myProps.join("&"));
    } else {
        emailWarning();
    }
}

function insert() {
    try {
        if (window.XMLHttpRequest) {
            xmlhttp = new XMLHttpRequest();
        } else {
            xmlhttp = new ActiveXObject('Microsoft.XMLHTTP');
        }


    var myProps = [];

    function addProp(id) {
            var value = encodeURIComponent(document.getElementById(id).value);
            myProps.push(id + "=" + value);
    }

    addProp('child_name');
    addProp('age');
    addProp('hometown');
    addProp('boy_girl');
        addProp('first_name');
    addProp('last_name');
    addProp('email');
    addProp('address1');
    addProp('address2');
    addProp('city');
    addProp('state');
    addProp('zip');
    addProp('country');

    var flagInvalid = false;
    var tempArray = document.getElementsByClassName("required");
    for (var i = 0; i < tempArray.length; i++) {
        if (tempArray[i].value == "") {
            flagInvalid = true;
            break;
        }
    }

    if (flagInvalid == false) {
        postData();

    } else {

        var log = document.getElementById("log");
        log.className = 'show';
        var log1 = document.getElementById("log1");
        log1.className = 'show';
        var log2 = document.getElementById("log2");
        log2.className = 'show';
        var log3 = document.getElementById("log3");
        log3.className = 'show';
        var log4 = document.getElementById("log4");
        log4.className = 'show';
        var log5 = document.getElementById("log5");
        log5.className = 'show';
        var log6 = document.getElementById("log6");
        log6.className = 'show';
        var log7 = document.getElementById("log7");
        log7.className = 'show';
        var log8 = document.getElementById("log8");
        log8.className = 'show';
        var log9 = document.getElementById("log9");
        log9.className = 'show';
        var log0 = document.getElementById("log0");
        log0.className = 'show';
        var logA = document.getElementById("logA");
        logA.className = 'show';
            }   

    } catch (e) {
        alert('An error occured in inert: ' + e);
    }

}

Upvotes: 4

Views: 6906

Answers (4)

justMe
justMe

Reputation: 11

if you get such error:

always check all your document.getElementById if they don't return null

var node = document.getElementById('someid');

if(node){
    do something;
}

but mark that

var node = document.getElementById('someid').value;

or

var node = document.getElementById('someid');

if(node.value){ 
    do something;
}

can still throw the error "can't read property of null", as you don't check if node really exists

Upvotes: 1

raina77ow
raina77ow

Reputation: 106375

The problem is easily catched when addProp body is changed to this:

function addProp(id) {
  var el = document.getElementById(id);
  if (el) {
    myProps.push(id + "=" + encodeURIComponent(el.value));
  }
  else {
    alert('Not found: ' + id);
  }
}

Both boy_girl and email IDs are not present in this HTML:

Boy: <input type="radio" name="boy_girl" id="boy_girl_b" value="boy"/>
Girl:<input type="radio" name="boy_girl" id="boy_girl_g" value="girl"/></li>
...
<input type="text" name="email" id="check" maxlength="64" class="required" />

You can fix it with something like this:

function addProp(name) {
    var els = document.getElementsByName(name);
    if (els.length) {
       myProps.push(name + "=" + encodeURIComponent(els[0].value));
    }
    else {
       alert('Not found: ' + name);
    }
}

But in fact, it's only the beginning of the story. myProps are local to insert function yet referenced in postData function; you show validation error signs for all the fields no matter what fields were actually filled... Besides, your code is a bit WET - for example, all these

            var log = document.getElementById("log");
            log.className = 'show';
            var log1 = document.getElementById("log1");
            log.className = 'show';
            ...

... can be easily transformed into this:

var showValidationError = function(id) {
    var el = document.getElementById(id);
    if (el) { 
        el.className = 'show'; 
    } 
    else { 
        alert('Missing element #' + id);
    }
}
...
showValidationError('log');
for (var i = 1; i < 10; i++) {
  showValidationError('log' + i);
}

I do understand that you're quite fresh with JS; but it's not about freshness, it's about organizing your code.

Upvotes: 2

epascarello
epascarello

Reputation: 207501

I am betting one of the addProp lines is not correct.

Debug this, see what is the last id before the error is thrown.

function addProp(id) {
        console.log(id);
        var value = encodeURIComponent(document.getElementById(id).value);
        myProps.push(id + "=" + value);
}

And when you do that, you will find out that the line

addProp('boy_girl');

will fail since there is no id

        <span id="log4" class="hidden" style="color:red"><b>*</b></span>
        Boy: <input type="radio" name="boy_girl" id="boy_girl_b" value="boy"/>
        Girl:<input type="radio" name="boy_girl" id="boy_girl_g" value="girl"/></li>

So let us change the function to check for id, and than check for the name if the id does not exist.

function addProp(id) {
    var input = document.getElementById(id);
    if (!input) {
        input = document.forms[0][id];
    }
    var value = encodeURIComponent(input.value);
    myProps.push(id + "=" + value);
}

Change it so myProps is outside of the function.

var myProps = [];  //<--- Added this line
function insert() {
        try {
            if (window.XMLHttpRequest) {
                xmlhttp = new XMLHttpRequest();
            } else {
                xmlhttp = new ActiveXObject('Microsoft.XMLHTTP');
            }


            myProps = [];  //<---- Changed this line

            function addProp(id) {
                var input = document.getElementById(id);
                if(!input) {
                   input = document.forms[0][id];   
                }
                console.log(input);
                var value = encodeURIComponent(input.value);
                myProps.push(id + "=" + value);
            }

            addProp('child_name');

Upvotes: 1

nja
nja

Reputation: 571

Make sure that you're designed IDs are existing on the page! For example boy_girl does not exist! Only boy_girl_band boy_girl_g The same applies for the mail. This one has the id check instead of mail.

Use Opera dragonfly or anything alike for basic troubleshooting

Upvotes: 0

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