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Attribute和Property的区别.md

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The Difference Between Attribute and Property

attribute is a concept in XML elements, used to describe additional information about XML tags, i.e., attributes of XML tags. property is a concept in JavaScript objects, used to describe members of JavaScript objects, i.e., properties of JavaScript objects.

Description

When describing HTML, we need to set key-value pairs for attribute values to describe tags:

<input id="this-input" type="text" value="test" />

The above tag node defines three attributes:

id: this-input
type: text
value: test

After the browser parses this HTML, it creates an Element object, which includes many properties such as id, innerHTML, outerHTML, etc. For this JavaScript object, many properties have the same or similar names as the attribute of this node element, but this is not a one-to-one relationship.

  • Some attributes have a one-to-one mapping with properties, such as the id attribute.
  • Some attributes have a one-to-one mapping with properties but with different names, such as the class attribute.
  • Some attributes do not have a mapping with properties, such as custom customize attributes.

Example

First, change the type in the <input> tag:

<input id="this-input" type="t" value="test" />

Now, get the attribute and property of the object using JavaScript:

console.log(document.querySelector("#this-input").getAttribute("type")); // t // attribute
console.log(document.querySelector("#this-input").type); // text // property

You can see that for properties, they automatically correct the incorrect value. For attributes, they retain the original value of the DOM node element. It can be said that attributes, semantically, tend to be immutable values, while properties, semantically, tend to be mutable values during their lifecycle. Here is another example, when changing the value in the input box from test to another value like t, and then getting the attribute and property:

console.log(document.querySelector("#this-input").getAttribute("value")); // test
console.log(document.querySelector("#this-input").value); // t
console.log(document.querySelector("#this-input").defaultValue); // test

You can see that the attribute still retains its original value, while the property gets the changed value. If you need to get the original value in the property, you can use the defaultValue property. If you customize some attributes in the DOM node, they may not be synchronized to the property, and similarly, properties defined in the property may not be synchronized to the attribute.

<input id="another-input" type="type" customize="test" />
console.log(document.querySelector("#another-input").customize); // undefined
console.log(document.querySelector("#another-input").getAttribute("customize")); // test

Code Example

<!DOCTYPE html>
<html>
<head>
    <title>Attribute Property</title>
</head>
<body>

    <input id="this-input" type="t" value="test" />
    <input id="another-input" type="type" customize="test" />

</body>
    <script type="text/javascript">
        console.log(document.querySelector("#this-input").type); // text
        console.log(document.querySelector("#this-input").getAttribute("type")); // t
        console.log(document.querySelector("#another-input").customize); // undefined
        console.log(document.querySelector("#another-input").getAttribute("customize")); // test
    </script>
</html>

Daily Question

https://github.com/WindrunnerMax/EveryDay

Reference

https://www.jianshu.com/p/8415edb391ce
https://juejin.im/post/5bea695ae51d45196e141f7f
https://stackoverflow.com/questions/6003819/what-is-the-difference-between-properties-and-attributes-in-html/6377829#6377829