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HTML - Output Element
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  Output Element Using For and Form Attributes

The following demo features an <output> element's use of the [for] and [form] attributes. Keep in mind, <output> needs JavaScript in order to function. Inline JavaScript is commonly used in forms as this example demonstrates. Although the <input> elements are type="number", their values are not numbers, they are text. So if you require the values to be calculated, you must convert each value into a number using methods such as: parseInt(), parseFloat(), Number(), etc.

Live Demo (opens new window)

   <!--form1 will collect the values of in1 and in2 on 'input' event.-->
    <!--out1 value will be the sum of in1 and in2 values.-->    

<form id="form1" name="form1" oninput="out1.value = parseInt(in1.value, 10) + parseInt(in2.value, 10)">

  <fieldset>

    <legend>Output Example</legend>

      <input type="number" id="in1" name="in1" value="0">
    <br/>
    +
    <input type="number" id="in2" name="in2" value="0">

  </fieldset>

</form>

<!--[for] attribute enables out1 to display calculations for in1 and in2.-->
<!--[form] attribute designates form1 as the form owner of out1 even if it isn't a descendant.-->

<output name="out1" for="in1 in2" form="form1">0</output>
  Output Element with Attributes 
<output name="out1" form="form1" for="inp1 inp2"></output>

Parameters

Attribute Description
Global Attributes that are available to any HTML5 element. For comprehensive documentation of these attributes see: MDN Global Attributes (opens new window)
name A string representing the name of an output. As a form element, output can be referenced by it's name using the document.forms property. This attribute is also used for collecting values on a form submit.
for A space separated list of form element ids (e.g. <inputs id="inp1"> for value is "inp1") that the output is meant to display calculations for.
form A string representing the <form> that is associated to the output. If the output is actually outside the <form>, this attribute will ensure that the output still belongs to the <form> and subject to collections and submits of said <form>.
 

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