Using a variable to define default value in a form input

Question

I have a variable called totaldue, which I want to use as the default value when submitting a form. I have the code

input type="number" name="sum-due" readonly="readonly" value=totaldue

But this doesn't display the content of totaldue in the form.

Is it possible to do this and if so what is the correct syntax?

Thx- Marie

Solution

You can't assign variable to textbox via HTML. Instead place the value directly

input type="number" name="sum-due" readonly="readonly" value="5"

This is only possible using javascript or jQuery.

For eg:

  <input id="my-input" type="number" name="sum-due" readonly="readonly" />

JS:

var totaldue = 5;
document.getElementById('my-input').value = totaldue;

UPDATES:

From your comments,

<script>
    var totaldue = 10;
    document.getElementById('paythis').value = totaldue;
</script>

<form id="pay1" action="hotguidebelize-com.cgi-data.com/webform/5627816.cgi"; method="post">
    <label>Total amount due:</label>
    <input id="paythis" type="number" name="sum-due" readonly="readonly" />
    <input type="submit" value="Proceed To Payment" />
</form>

As I said before you can't assign variable to textbox via HTML. Following are the mistakes:

(1) There is no variable totaldue assigned in your javascript.

var totaldue = 5;

(2) Try using <label> tag. More Information from MDN.

(3) You're using document.getElementById which refers id selector. But you haven't specified the id in your input tag. More Information from MDN

<input id="paythis" type="number" name="sum-due" readonly="readonly" />

Here is simple JSFiddle I have created for you.

Feel free to ask your doubts, when I get time I will reply back or you will get help from others.

Comments

[Brandon Joyce]

Is this a javascript variable, or a server language variable?

[Praveen]

@jeconner Thanks for the fiddle.

[Marie Carroll Rigby]

As a total newbie I am lost. So I know have <script> document.getElementById('paythis').value = totaldue; </script> <form id="pay1" action="hotguidebelize-com.cgi-data.com/webform/5627816.cgi" method="post"> Total amount due: <input type="number" name="sum-due" readonly="readonly" value=paythis> <input type="submit" value="Proceed To Payment" /> </form> but it just displays the word paythis and not the number from the variable. I know this is probably really basic stuff but I'm not getting it!

[Praveen]

@MarieCarrollRigby Updated my answer. Take time to learn things.

[JoBaxter]

One comment about the script part of the code. You can save a line by assigning the return value directly to the field. For example. <script>document.getElementById('paythis').value = 10;</script>