HTML form input tag name element array with JavaScript

Question

This is a two part question. Someone answered a similar question the other day (which also contained info about this type of array in PHP), but I cannot find it.

1.) First off, what is the correct terminology for an array created on the end of the name element of an input tag in a form?

<form>

    <input name="p_id[]" value="0"/>
    <input name="p_id[]" value="1"/>
    <input name="p_id[]" value="2"/>

</form>

2.) How do I get the information from that array with JavaScript? Specifically, I am right now just wanting to count the elements of the array. Here is what I did but it isn't working.

function form_check(){
    for(var i = 0; i < count(document.form.p_id[]); i++){  //Error on this line

        if (document.form.p_name[i].value == ''){
            window.alert('Name Message');
            document.form.p_name[i].focus();
            break;
        }

        else{
            if (document.form.p_price[i].value == ''){
                window.alert('Price Message');
                document.form.p_price[i].focus();
                break;
            }

            else{
                update_confirmation();
            }
        }
    }
}

Solution 1

1.) First off, what is the correct terminology for an array created on the end of the name element of an input tag in a form?

"Oftimes Confusing PHPism"

As far as JavaScript is concerned a bunch of form controls with the same name are just a bunch of form controls with the same name, and form controls with names that include square brackets are just form controls with names that include square brackets.

The PHP naming convention for form controls with the same name is sometimes useful (when you have a number of groups of controls so you can do things like this:

<input name="name[1]">
<input name="email[1]">
<input name="sex[1]" type="radio" value="m">
<input name="sex[1]" type="radio" value="f">

<input name="name[2]">
<input name="email[2]">
<input name="sex[2]" type="radio" value="m">
<input name="sex[2]" type="radio" value="f">

) but does confuse some people. Some other languages have adopted the convention since this was originally written, but generally only as an optional feature. For example, via this module for JavaScript.

2.) How do I get the information from that array with JavaScript?

It is still just a matter of getting the property with the same name as the form control from elements. The trick is that since the name of the form controls includes square brackets, you can't use dot notation and have to use square bracket notation just like any other JavaScript property name that includes special characters.

Since you have multiple elements with that name, it will be a collection rather then a single control, so you can loop over it with a standard for loop that makes use of its length property.

var myForm = document.forms.id_of_form;
var myControls = myForm.elements['p_id[]'];
for (var i = 0; i < myControls.length; i++) {
    var aControl = myControls[i];
}

Solution 2

Try this something like this:

var p_ids = document.forms[0].elements["p_id[]"];
alert(p_ids.length);
for (var i = 0, len = p_ids.length; i < len; i++) {
  alert(p_ids[i].value);
}

Solution 3

document.form.p_id.length ... not count().

You really should give your form an id

<form id="myform">

Then refer to it using:

var theForm = document.getElementById("myform");

Then refer to the elements like:

for(var i = 0; i < theForm.p_id.length; i++){

Solution 4

To answer your questions in order:
1) There is no specific name for this. It's simply multiple elements with the same name (and in this case type as well). Name isn't unique, which is why id was invented (it's supposed to be unique).
2)

function getElementsByTagAndName(tag, name) {
    //you could pass in the starting element which would make this faster
    var elem = document.getElementsByTagName(tag);  
    var arr = new Array();
    var i = 0;
    var iarr = 0;
    var att;
    for(; i < elem.length; i++) {
        att = elem[i].getAttribute("name");
        if(att == name) {
            arr[iarr] = elem[i];
            iarr++;
        }
    }
    return arr;
}

View more solutions

Comments

[Quentin]

Wow. That's just ugly. Using new Array() instead of [], keeping a length tracker instead of using arr.length or arr.push(), initializing i outside the for loop, using getAttribute instead of just going for the name property, working globally instead of within a form, and all the get (more or less) the same results of document.forms.element.elements_name. (Oh and getElementsByName could have been used too).

[ubiquibacon]

Thanks, this is exactly what I was looking for. I modified it a little though... for(i = 0; i < document.form.elements['p_id[]'].length; i++)

[Quentin]

Using i as a global isn't a good idea (it is just asking for scoping issues to bite you, either now or in the future because you have got into bad habits). Using document.form is bad practice because (a) the document.forms collection will make it clearer what you are doing and form isn't a very detailed name (and document.form could be confused with document.forms which makes maintenance more confusing. Scrunching things up on to a single line is fine though, I was just more explicit so you could see what is going on.

[Laoujin]

@Quentin: for (var i...) is in fact the same as var i; for (i ...) because JavaScript variables are function scoped, not block-scoped as is the case in many popular OO-languages.

[Quentin]

@Laoujin — typoknig didn't say var i; for (i ...) though.

[Michael Julyus Christopher M.]

I have a problem when the form element is drop-down list. Can you give me solution for my question in stackoverflow.com/questions/58994834/…