How can i validate the input from a html5 Datalist?

Question

I would like to know how I can validate the input value that comes from a Datalist. I mean, if I have a Datalist where the user can start to write a value and then choosing it from the Datalist, but the user decides to don't choose any value from the list and he submits the form with the incomplete value, the sent value will be wrong.

I thought about iterate over all the elements of the Datalist but I think that it can't be a good idea if the Datalist has more than 1.000 values and I don't know any other way to validate it.

Here is an example of the Datalist that I'm going to use:

<input type="text" list="colours">

<datalist id="colours">
    <option value="Red" data-id="1">
    <option value="Blue" data-id="2">
    <option value="Green" data-id="3">
    <option value="Black" data-id="4">
    <option value="White" data-id="5">
</datalist>

Answer 1

Try this:

<input type="text" list="colours" id='txt'>

And on form submit you can check:

var val = $("#txt").val();

var obj = $("#colours").find("option[value='" + val + "']");

if(obj != null && obj.length > 0)
    alert("valid");  // allow form submission
else
    alert("invalid"); // don't allow form submission

Answer 2

You can do this with HTML5 validation using pattern. It's easier if you're populating your datalist with some sort of template, but it would look something like this (Note that you would need additional code to handle the validation - I just added very simple CSS to display the validation state)

It's worth noting that this automatically blocks form submission and provides proper semantics for accessibility and other standards-compliant interoperability.

input:valid {
  border: 1px solid green;
}
input:invalid {
  border: 1px solid red;
}

<input type="text" list="colours"
pattern="^(Red|Blue|Green|Black|White)$"
>

<datalist id="colours">
    <option value="Red" data-id="1">
    <option value="Blue" data-id="2">
    <option value="Green" data-id="3">
    <option value="Black" data-id="4">
    <option value="White" data-id="5">
</datalist>