How to set HTML5's required attribute using Javascript?

Question

I'm trying to mark a text input box as required in Javascript.

<input id="edName" type="text" id="name">

If the field was originally marked required:

<form>
    <input id="edName" type="text" id="name" required><br>
    <input type="submit" value="Search">
</form>

When the user attempts to submit, they receive a validation error:

But now I want to set the required property at "runtime" via Javascript:

<form>
    <input id="edName" type="text" id="name"><br>
    <input type="submit" value="Search">
</form>

Use the corresponding script:

//recommended W3C HTML5 syntax for boolean attributes
document.getElementById("edName").attributes["required"] = "";

No validation checks, no blocking unless I submit now.

Settings What is the correct way to validate Boolean attributes in HTML5?

jsFiddle

What is the value of this attribute you ask?

HTML5 Validation required Attributes logged as Boolean:

4.10.7.3.4 required Properties

required The property is a Boolean property. When specified, this element is required.

There are a lot of annoying things about how to define boolean properties. HTML5 specification comments:

The presence of a Boolean attribute on the

element represents a true value, and the absence of this attribute represents a false value.

If the attribute is present, its value must be the empty string or an ASCII case-insensitive value that matches the attribute's canonical name and has no leading or trailing spaces.

This means you can specify the required boolean attribute in two different ways:

edName.attributes.required = ""; //the empty string
edName.attributes.required = "required"; //the attribute's canonical name

But what is the value of the attribute actually?

When you look at my jsFiddle for this question, you'll notice that if the required attribute is defined in the tag:

<input id="edName" type="text" id="name" required>

Then the value of the attribute is not an empty string , nor is it the canonical name of the attribute:

edName.attributes.required = [object Attr]

This may lead to a solution.

Answer 1

required is a reflective attribute (e.g. id, name, type, etc.), so:

element.required = true;

...where element is the actual input DOM element, for example:

document.getElementById("edName").required = true;

---

(Just for completeness.)

reply:

That's because required in this code is a property object, not a string; property isNamedNodeMap Its value is Attr代码>object. To get the value of one of these, you need to look at its value property. But for boolean properties, the value is irrelevant; the property is either present in the map (true) or not (false).

So if required is not reflected, you can set it by adding the attribute:

element.setAttribute("required", "");

...Equivalent to element.required = true. You can clear it by deleting it completely:

element.removeAttribute("required");

...Equivalent to element.required = false.

But we don't have to do this for required because it's already reflected.

Answer 2

Short version

element.setAttribute("required", "");    //turns required on
element.required = true;                 //turns required on through reflected attribute
jQuery(element).attr('required', '');    //turns required on
$("#elementId").attr('required', '');    //turns required on

element.removeAttribute("required");     //turns required off
element.required = false;                //turns required off through reflected attribute
jQuery(element).removeAttr('required');  //turns required off
$("#elementId").removeAttr('required');  //turns required off

if (edName.hasAttribute("required")) { }  //check if required
if (edName.required) { }                 //check if required using reflected attribute

Long version

Once T.J. Crowder managed to point out the reflected properties, I learned the following syntax error:

element.attributes["name"] = value; //bad! Overwrites the HtmlAttribute object
element.attributes.name = value;    //bad! Overwrites the HtmlAttribute object
value = element.attributes.name;    //bad! Returns the HtmlAttribute object, not its value
value = element.attributes["name"]; //bad! Returns the HtmlAttribute object, not its value

You must pass element.getAttribute and element.setAttribute:

element.getAttribute("foo");         //correct
element.setAttribute("foo", "test"); //correct

This is because the attribute actually contains a special HtmlAttribute object:

element.attributes["foo"];           //returns HtmlAttribute object, not the value of the attribute
element.attributes.foo;              //returns HtmlAttribute object, not the value of the attribute

By setting the attribute value to "true", you are mistakenly setting it to a String object instead of the HtmlAttribute object it requires:

element.attributes["foo"] = "true";  //error because "true" is not a HtmlAttribute object
element.setAttribute("foo", "true"); //error because "true" is not an HtmlAttribute object

Conceptually, the correct idea (expressed in type language) is:

HtmlAttribute attribute = new HtmlAttribute();
attribute.value = "";
element.attributes["required"] = attribute;

Here’s why:

• getAttribute(name)
• setAttribute(name, value)

exist. They are responsible for assigning values ​​to the internal HtmlAttribute objects.

In addition, it also reflects some attributes. This means you have better access to them via Javascript:

//Set the required attribute
//element.setAttribute("required", ""); 
element.required = true;

//Check the attribute
//if (element.getAttribute("required")) {...}
if (element.required) {...}

//Remove the required attribute
//element.removeAttribute("required");
element.required = false;

What you don't want to do is incorrectly use the .attributes collection:

element.attributes.required = true;     //WRONG!
if (element.attributes.required) {...}  //WRONG!
element.attributes.required = false;    //WRONG!

Test Case

This results in testing around the use of the required attribute, comparing the value returned via that attribute to the reflected attribute

document.getElementById("name").required;
document.getElementById("name").getAttribute("required");

result:

HTML                         .required        .getAttribute("required")
==========================   ===============  =========================
                      false (Boolean)  null (Object)
             true  (Boolean)  "" (String)
          true  (Boolean)  "" (String)
  true  (Boolean)  "required" (String)
      true  (Boolean)  "true" (String)
     true  (Boolean)  "false" (String)
         true  (Boolean)  "0" (String)

It is an error to attempt to access the .attributes collection directly. It returns an object representing a DOM property:

edName.attributes["required"] => [object Attr]
edName.attributes.required    => [object Attr]

This explains why you should never talk directly to the .attributes collection. You are not manipulating the value of the property, you are manipulating the object that represents the property itself.

How to set required fields?

What is the correct way to set required on a property? You have two options, either reflected properties or by setting the properties correctly:

element.setAttribute("required", "");         //Correct
element.required = true;                      //Correct

Strictly speaking, any other value will "set" the property. However, the definition of the Boolean property states that it can only be set to the empty string "" to indicate true. The following methods can set the requiredBoolean attribute,

But don’t use them:

element.setAttribute("required", "required"); //valid, but not preferred
element.setAttribute("required", "foo");      //works, but silly
element.setAttribute("required", "true");     //Works, but don't do it, because:
element.setAttribute("required", "false");    //also sets required boolean to true
element.setAttribute("required", false);      //also sets required boolean to true
element.setAttribute("required", 0);          //also sets required boolean to true

We have learned that it is an error to try to set the property directly:

edName.attributes["required"] = true;       //wrong
edName.attributes["required"] = "";         //wrong
edName.attributes["required"] = "required"; //wrong
edName.attributes.required = true;          //wrong
edName.attributes.required = "";            //wrong
edName.attributes.required = "required";    //wrong

How to clear required fields?

TryRemove required The trick when using an attribute is that it's easy to accidentally open it:

edName.removeAttribute("required");     //Correct
edName.required = false;                //Correct

Invalid method:

edName.setAttribute("required", null);    //WRONG! Actually turns required on!
edName.setAttribute("required", "");      //WRONG! Actually turns required on!
edName.setAttribute("required", "false"); //WRONG! Actually turns required on!
edName.setAttribute("required", false);   //WRONG! Actually turns required on!
edName.setAttribute("required", 0);       //WRONG! Actually turns required on!

When using reflection's .required property, you can also use any "falsey" value to turn it off and use a true value to turn it on. But for the sake of clarity, stick to right and wrong.

How to check if is required?

Check whether the attribute exists through the .hasAttribute("required") method:

if (edName.hasAttribute("required"))
{
}

You can also check via the Boolean reflected .required property:

if (edName.required)
{
}