<label for="camp-week">Choose a week in May or June:</label><input  type="week"  name="week"   min="2018-W18"  max="2018-W26"  required />

label {  display: block;  font:    1rem "Fira Sans",    sans-serif;}input,label {  margin: 0.4rem 0;}

The control's user interface varies from browser to browser; cross-browser support is currently a bit limited, with only Chrome/Opera and Microsoft Edge supporting it at this time. In non-supporting browsers, the control degrades gracefully to function identically to<input type="text">.

A string representing the value of the week/year entered into the input. The format of the date and time value used by this input type is described inWeek strings.

You can set a default value for the input by including a value inside thevalue attribute, like so:

<label for="week">What week would you like to start?</label><input type="week" name="week" value="2017-W01" />

One thing to note is that the displayed format may differ from the actualvalue, which is always formattedyyyy-Www. When the above value is submitted to the server, for example, browsers may display it asWeek 01, 2017, but the submitted value will always look likeweek=2017-W01.

You can also get and set the value in JavaScript using the input element'svalue property, for example:

const weekControl = document.querySelector('input[type="week"]');weekControl.value = "2017-W45";

In addition to the attributes common to<input> elements, week inputs offer the following attributes.

The latest (time-wise) year and week number, in the string format discussed in theValue section above, to accept. If thevalue entered into the element exceeds this, the element failsconstraint validation. If the value of themax attribute isn't a valid week string, then the element has no maximum value.

This value must be greater than or equal to the year and week specified by themin attribute.

The earliest year and week to accept. If thevalue of the element is less than this, the element failsconstraint validation. If a value is specified formin that isn't a valid week string, the input has no minimum value.

This value must be less than or equal to the value of themax attribute.

A Boolean attribute which, if present, means this field cannot be edited by the user. Itsvalue can, however, still be changed by JavaScript code directly setting theHTMLInputElementvalue property.

Thestep attribute is a number that specifies the granularity that the value must adhere to, or the special valueany, which is described below. Only values which are equal to the basis for stepping (min if specified,value otherwise, and an appropriate default value if neither of those is provided) are valid.

A string value ofany means that no stepping is implied, and any value is allowed (barring other constraints, such asmin andmax).

Forweek inputs, the value ofstep is given in weeks, with a scaling factor of 604,800,000 (since the underlying numeric value is in milliseconds). The default value ofstep is 1, indicating 1week. The default stepping base is -259,200,000, which is the beginning of the first week of 1970 ("1970-W01").

At this time, it's unclear what a value of"any" means forstep when used withweek inputs. This will be updated as soon as that information is determined.

Week inputs sound convenient at first glance, since they provide an easy UI for choosing weeks, and they normalize the data format sent to the server, regardless of the user's browser or locale. However, there are issues with<input type="week"> because browser support is not guaranteed across all browsers.

We'll look at basic and more complex uses of<input type="week">, then offer advice on mitigating the browser support issue later on (seeHandling browser support).

The most basic use of<input type="week"> involves a basic<input> and<label> element combination, as seen below:

<form>  <label for="week">What week would you like to start?</label>  <input type="week" name="week" /></form>

<input type="week"> doesn't support form sizing attributes such assize. You'll have to resort toCSS for sizing needs.

You should be able to use thestep attribute to vary the number of weeks jumped whenever they are incremented or decremented, however it doesn't seem to have any effect on supporting browsers.

By default,<input type="week"> does not apply any validation to entered values. The UI implementations generally don't let you specify anything that isn't a valid week/year, which is helpful, but it's still possible to submit with the field empty, and you might want to restrict the range of choosable weeks.

You can use themin andmax attributes to restrict the valid weeks that can be chosen by the user. In the following example we are setting a minimum value ofWeek 01, 2017 and a maximum value ofWeek 52, 2017:

<form>  <label for="week">What week would you like to start?</label>  <input type="week" name="week" min="2017-W01" max="2017-W52" />  <span></span></form>

Here's the CSS used in the above example. Here we make use of the:valid and:invalid CSS properties to style the input based on whether the current value is valid. We had to put the icons on a<span> next to the input, not on the input itself, because in Chrome the generated content is placed inside the form control, and can't be styled or shown effectively.

div {  margin-bottom: 10px;  position: relative;}input[type="number"] {  width: 100px;}input + span {  padding-right: 30px;}input:invalid + span::after {  position: absolute;  content: "✖";  padding-left: 5px;}input:valid + span::after {  position: absolute;  content: "✓";  padding-left: 5px;}

The result here is that only weeks between W01 and W52 in 2017 will be seen as valid and be selectable in supporting browsers.

In addition you can use therequired attribute to make filling in the week mandatory. As a result, supporting browsers will display an error if you try to submit an empty week field.

Let's look at an example; here we've set minimum and maximum weeks, and also made the field required:

<form>  <div>    <label for="week">What week would you like to start?</label>    <input           type="week"      name="week"      min="2017-W01"      max="2017-W52"      required />    <span></span>  </div>  <div>    <input type="submit" value="Submit form" />  </div></form>

If you try to submit the form with no value, the browser displays an error. Try playing with the example now:

Here is a screenshot for those of you who aren't using a supporting browser:

As mentioned above, the major problem with using week inputs right now is browser support: Safari and Firefox don't support it on desktop, and old versions of IE don't support it.

Mobile platforms such as Android and iOS make perfect use of such input types, providing specialist UI controls that make it really easy to select values in a touchscreen environment. For example, theweek picker on Chrome for Android looks like this:

Non-supporting browsers gracefully degrade to a text input, but this creates problems both in terms of consistency of user interface (the presented control will be different), and data handling.

The second problem is the more serious. As mentioned earlier, with aweek input the actual value is always normalized to the formatyyyy-Www. When the browser falls back to a generic text input, there's nothing to guide the user toward correctly formatting the input (and it's certainly not intuitive). There are multiple ways in which people could write week values; for example:

• Week 1 2017
• Jan 2-8 2017
• 2017-W01
• etc.

The best way to deal with week/years in forms in a cross-browser way at the moment is to get the user to enter the week number and year in separate controls (<select> elements being popular; see below for an example), or use JavaScript libraries such asjQuery date picker.

In this example we create two sets of UI elements for choosing weeks: a native picker created using<input type="week">, and a set of two<select> elements for choosing weeks/years in older browsers that don't support theweek input type.

The HTML looks like so:

<form>  <div>    <label for="week">What week would you like to start?</label>    <input           type="week"      name="week"      min="2017-W01"      max="2018-W52"      required />    <span></span>  </div>  <p>What week would you like to start?</p>  <div>    <div>      <span>        <label for="week">Week:</label>        <select name="week"></select>      </span>      <span>        <label for="year">Year:</label>        <select name="year">          <option value="2017" selected>2017</option>          <option value="2018">2018</option>        </select>      </span>    </div>  </div></form>

The week values are dynamically generated by the JavaScript code below.

div {  margin-bottom: 10px;  position: relative;}input[type="number"] {  width: 100px;}input + span {  padding-right: 30px;}input:invalid + span::after {  position: absolute;  content: "✖";  padding-left: 5px;}input:valid + span::after {  position: absolute;  content: "✓";  padding-left: 5px;}

The other part of the code that may be of interest is the feature detection code. To detect whether the browser supports<input type="week">, we create a new<input> element, try setting itstype toweek, then immediately check what itstype is set to. Non-supporting browsers will returntext, because theweek type falls back to typetext. If<input type="week"> is not supported, we hide the native picker and show the fallback picker UI (<select>s) instead.

// Get UI elementsconst nativePicker = document.querySelector(".nativeWeekPicker");const fallbackPicker = document.querySelector(".fallbackWeekPicker");const fallbackLabel = document.querySelector(".fallbackLabel");const yearSelect = document.querySelector("#year");const weekSelect = document.querySelector("#fallbackWeek");// Hide fallback initiallyfallbackPicker.style.display = "none";fallbackLabel.style.display = "none";// Test whether a new date input falls back to a text input or notconst test = document.createElement("input");try {  test.type = "week";} catch (e) {  console.log(e.description);}// If it does, run the code inside the if () {} blockif (test.type === "text") {  // Hide the native picker and show the fallback  nativePicker.style.display = "none";  fallbackPicker.style.display = "block";  fallbackLabel.style.display = "block";  // populate the weeks dynamically  populateWeeks();}function populateWeeks() {  // Populate the week select with 52 weeks  for (let i = 1; i <= 52; i++) {    const option = document.createElement("option");    option.textContent = i < 10 ? `0${i}` : i;    weekSelect.appendChild(option);  }}

• The generic<input> element and the interface used to manipulate it,HTMLInputElement
• Date and time formats used in HTML
• <input type="datetime-local">,<input type="date">,<input type="time">, and<input type="month">