JavaScript - Getting HTML form values

How can I get the value of an HTML form to pass to JavaScript?

Is this correct? My script takes two arguments one from textbox, one from the dropdown box.

<body>
<form name="valform" action="" method="POST">

Credit Card Validation: <input type="text" id="cctextboxid" name="cctextbox"><br/>
Card Type: <select name="cardtype" id="cardtypeid">
  <option value="visa">Visa</option>
  <option value="mastercard">MasterCard</option>
  <option value="discover">Discover</option>
  <option value="amex">Amex</option>
  <option value="diners">Diners Club</option>
</select><br/>
<input type="button" name="submit" value="Verify Credit Card" onclick="isValidCreditCard(document.getElementById('cctextboxid').value,document.getElementById('cardtypeid').value)" />
</body>

Answers:

Answer

document.forms will contain an array of forms on your page. You can loop through these forms to find the specific form you desire.

var form = false;
var length = document.forms.length;
for(var i = 0; i < length; i++) {
    if(form.id == "wanted_id") {
        form = document.forms[i];
    }
}

Each form has an elements array which you can then loop through to find the data that you want. You should also be able to access them by name

var wanted_value = form.someFieldName.value;
jsFunction(wanted_value);
Answer

Several easy-to-use form serializers with good documentation.

In order of Github stars,

  1. jquery.serializeJSON

  2. jquery-serialize-object

  3. form2js

  4. form-serialize

Answer

My 5 cents here, using form.elements which allows you to query each field by it's name, not only by iteration:

const form = document.querySelector('form[name="valform"]');
const ccValidation = form.elements['cctextbox'].value;
const ccType = form.elements['cardtype'].value;
Answer

HTML:

<input type="text" name="name" id="uniqueID" value="value" />

JS:

var nameValue = document.getElementById("uniqueID").value;
Answer

If you want to retrieve the form values (such as those that would be sent using an HTTP POST) you can use:

JavaScript

new FormData(document.querySelector('form'))

form-serialize (https://code.google.com/archive/p/form-serialize/)

serialize(document.forms[0]);

jQuery

$("form").serializeArray()
Answer

Here is an example from W3Schools:

function myFunction() {
    var elements = document.getElementById("myForm").elements;
    var obj ={};
    for(var i = 0 ; i < elements.length ; i++){
        var item = elements.item(i);
        obj[item.name] = item.value;
    }

    document.getElementById("demo").innerHTML = JSON.stringify(obj);
}

The demo can be found here.

Answer
<input type="text" id="note_text" />

let value = document.getElementById("note_text").value;
Answer

Expanding on Atrur Klesun's idea... you can just access it by its name if you use getElementById to reach the form. In one line:

document.getElementById('form_id').elements['select_name'].value;

I used it like so for radio buttons and worked fine. I guess it's the same here.

Answer

This is a developed example of https://stackoverflow.com/a/41262933/2464828

Consider

<form method="POST" enctype="multipart/form-data" onsubmit="return check(event)">
    <input name="formula">
</form>

Let us assume we want to retrieve the input of name formula. This can be done by passing the event in the onsubmit field. We can then use FormData to retrieve the values of this exact form by referencing the SubmitEvent object.

const check = (e) => {
    const form = new FormData(e.target);
    const formula = form.get("formula");
    console.log(formula);
    return false
};

The JavaScript code above will then print the value of the input to the console.

If you want to iterate the values, i.e., get all the values, then see https://developer.mozilla.org/en-US/docs/Web/API/FormData#Methods

Answer

Please try to change the code as below:

<form
   onSubmit={e => {
     e.preventDefault();
     e.stopPropagation();

     const elements = Array.from(e.currentTarget) as HTMLInputElement[];

     const state = elements.reduce((acc, el) => {
       if (el.name) {
         acc[el.name] = el.value;
       }

       return acc;
     }, {});

     console.log(state); // {test: '123'}
   }}
>
   <input name='test' value='123' />
</form>
Answer

Quick solution to serialize a form without any libraries

function serializeIt(form) {
  return (
    Array.apply(0, form.elements).map(x => 
      (
        (obj => 
          (
            x.type == "radio" ||
            x.type == "checkbox"
          ) ?
            x.checked ? 
              obj
            : 
              null
          :
            obj
        )(
          {
            [x.name]:x.value
          }
        )
      )
    ).filter(x => x)
  );
}

function whenSubmitted(e) {
  e.preventDefault()
  console.log(
    JSON.stringify(
      serializeIt(document.forms[0]),
      4, 4, 4
    )
  )
}
<form onsubmit="whenSubmitted(event)">
<input type=text name=hiThere value=nothing>
<input type=radio name=okRadioHere value=nothin>
<input type=radio name=okRadioHere1 value=nothinElse>
<input type=radio name=okRadioHere2 value=nothinStill>

<input type=checkbox name=justAcheckBox value=checkin>
<input type=checkbox name=justAcheckBox1 value=checkin1>
<input type=checkbox name=justAcheckBox2 value=checkin2>

<select name=selectingSomething>
<option value="hiThere">Hi</option>
<option value="hiThere1">Hi1</option>
<option value="hiThere2">Hi2</option>
<option value="hiThere3">Hi3</option>
</select>
<input type=submit value="click me!" name=subd>
</form>

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