Deep understanding of HTML forms

Form elements

From HTML to HTML5, form-related elements have been greatly expanded and can basically meet our common needs. . But in actual work, Due to interaction or browser compatibility requirements, native form elements sometimes have to be extended or simulated. But before that, it is still important to clearly understand and master the various form elements. in the text, We will explain form elements (HTML5 form elements by default) in detail.

form

##● The form will automatically handle the submit event (the submit event is usually triggered by the input or button element of type=submit)

●The form will automatically do a layer of verification, and use form.novalidate to turn off the native validate

●Form will obtain the corresponding user input based on the name of each form element, and then add the form data in the form of query string to the end of the URL corresponding to the action attribute. The default request method is GET, and the default action is the current url.

●event.target.elements will return all interactive elements

<form novalidate>
  <input name=&#39;username&#39; required/>
  <input name=&#39;passworkd&#39; type=&#39;password&#39; required/>
  <input name=&#39;email&#39; type=&#39;email&#39;/>
  <input type=&#39;submit&#39; value=&#39;submit&#39;/>
</form>

You can see by running the above code that after submitting the form, the browser address will Add a query string like this?username=tom&passworkd=123&email=test%40gmail.com

Interactive elements

Need to interact with the user and obtain user input We classify this type of form elements as interactive form elements.

Some are listed below:

●input: Commonly used types include checkbox, tel, number, email, etc.

●textarea

●select

●option

Feedback elements

Form elements that simply feed back information and do not require interaction with the user, we classify them as Feedback form element.

Some are listed below:

●meter

●output

<form oninput="result.value=parseInt(a.value)+parseInt(b.value)">
    <input type=&#39;number&#39; value=&#39;50&#39; name=&#39;a&#39; />
    <input type=&#39;number&#39; value=&#39;10&#39; name=&#39;b&#39; />
    <output name=&#39;result&#39;>60</output>
</form>

For output, you can set the calculated value in form.oninput

Grouped elements

This type of form element is used to group multiple form elements. We classify them as grouped form elements.

Some are listed below:

●fieldset

●optgroup

<form>
  <select>
    <optgroup label=&#39;group1&#39;>
      <option>1</option>
      <option>2</option>
      <option>3</option>
    </optgroup>
    <optgroup label=&#39;group2&#39;>
      <option>4</option>
      <option>5</option>
      <option>6</option>
    </optgroup>
    <optgroup label=&#39;group3&#39;>
      <option>7</option>
      <option>8</option>
      <option>9</optioin>
    </optgroup>
  </select>
</form>

label

●Use for can be connected to the corresponding interactive element associated with the id

●Can be used to wrap interactive elements, including multiple, control the first one

●It is not recommended to nest labels

<form>
  <fieldset>
    <legend>Title</legend>
    <label for=&#39;radio&#39;>Click me</label>
    <input type=&#39;radio&#39; id=&#39;radio&#39;/>
  </fieldset>
</form>

<form>
  <fieldset>
    <legend>用户信息</legend>
    <label>
      男 <input type=&#39;radio&#39; name=&#39;gender&#39; id=&#39;male&#39; />
    </label>
    <label>
      女 <input type=&#39;radio&#39; name=&#39;gender&#39; id=&#39;female&#39;/>
    </label>
  </fieldset>
</form>

Use JavaScript to process forms

Abstraction of field

The most basic structure:

 field: {
    name: String,
    value: String || String[]
  }

● String[] of value is usually used, and is divided and synthesized into a String

●For names with complex structures, you can use keyPath

  const fromKeyValues = {
    'user.name': 'Tom',
    'user.phone[0].number': '123456',
    'user.phone[0].type': 'mobile'
  };

  const fromValues = {
    user: {
      name: 'Tom',
      phone: [
        {
          number: '123456',
          type: 'mobile'
        }
      ]
    }
  };

If you are not very clear about the above code, please refer to qs

A complete implementation

●Prevent form from default submit event

●checkbox needs to be checked instead of value

● select-multiple needs to store multiple values

●Except for the above special interactive elements, the others take their values ​​from value by default

form.html

<form>
    <fieldset>
        <legend>Login</legend>
        <input name=&#39;username&#39; placeholder=&#39;username&#39; minlength=&#39;2&#39;/>
        <input name=&#39;password&#39; type=&#39;password&#39; placeholder=&#39;password&#39;/>
        <label>
            remember password            <input name=&#39;checkbox&#39; type=&#39;checkbox&#39;/>
        </label>
    </fieldset>
    <fieldset>
        <p class="gender">
            <legend>More Info</legend>
            <label>
                男                <input name=&#39;gender&#39; type=&#39;radio&#39; value=&#39;male&#39; />
            </label>
            <label>
                女                <input name=&#39;gender&#39; type=&#39;radio&#39; value=&#39;female&#39; />
            </label>
        </p>
        <select name=&#39;select&#39; multiple>
            <option>1</option>
            <optgroup label=&#39;2&#39;>
                <option>2.1</option>
                <option>2.2</option>
            </optgroup>
        </select>
    </fieldset>
    <button type=&#39;submit&#39;>Submit</button></form>

form.js

var $form = document.querySelector('form');

function getFormValues(form) {
  var values = {};
  var elements = form.elements; // elemtns is an array-like object

  for (var i = 0; i < elements.length; i++) {
    var input = elements[i];
    if (input.name) {
      switch (input.type.toLowerCase()) {
        case &#39;checkbox&#39;:
          if (input.checked) {
            values[input.name] = input.checked;
          }
          break;
        case &#39;select-multiple&#39;:
          values[input.name] = values[input.name] || [];
          for (var j = 0; j < input.length; j++) {
            if (input[j].selected) {
              values[input.name].push(input[j].value);
            }
          }
          break;
        default:
          values[input.name] = input.value;
          break;
      }
    }

  }

  return values;
}

$form.addEventListener(&#39;submit&#39;, function(event) {
  event.preventDefault();
  getFormValues(event.target);
  console.log(event.target.elements);
  console.log(getFormValues(event.target));
});