HTML is designed with extensibility in mind for data that should be associated with a particular element but need not have any defined meaning. data-* attributes allow us to store extra information on standard, semantic HTML elements without other hacks such as non-standard attributes, or extra properties on DOM.

The syntax is simple. Any attribute on any element whose attribute name starts with data- is a data attribute. Say you have an article and you want to store some extra information that doesn't have any visual representation. Just use data attributes for that:


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Reading the values of these attributes out in JavaScript is also very simple. You could use getAttribute() with their full HTML name to read them, but the standard defines a simpler way: a DOMStringMap you can read out via a dataset property.

Note that, as data attributes are plain HTML attributes, you can even access them from CSS. For example to show the parent data on the article you can use generated content in CSS with the attr() function:

Programming languages all have built-in data structures, but these often differ from one language to another. This article attempts to list the built-in data structures available in JavaScript and what properties they have. These can be used to build other data structures.

The String type represents textual data and is encoded as a sequence of 16-bit unsigned integer values representing UTF-16 code units. Each element in the string occupies a position in the string. The first element is at index 0, the next at index 1, and so on. The length of a string is the number of UTF-16 code units in it, which may not correspond to the actual number of Unicode characters; see the String reference page for more details.

With conventions, it is possible to represent any data structure in a string. This does not make it a good idea. For instance, with a separator, one could emulate a list (while a JavaScript array would be more suitable). Unfortunately, when the separator is used in one of the "list" elements, then, the list is broken. An escape character can be chosen, etc. All of this requires conventions and creates an unnecessary maintenance burden.

In JavaScript, objects can be seen as a collection of properties. With the object literal syntax, a limited set of properties are initialized; then properties can be added and removed. Object properties are equivalent to key-value pairs. Property keys are either strings or symbols. Property values can be values of any type, including other objects, which enables building complex data structures.

There are two types of object properties: The data property and the accessor property. Each property has corresponding attributes. Each attribute is accessed internally by the JavaScript engine, but you can set them through Object.defineProperty(), or read them through Object.getOwnPropertyDescriptor(). You can read more about the various nuances on the Object.defineProperty() page.

Objects are ad-hoc key-value pairs, so they are often used as maps. However, there can be ergonomics, security, and performance issues. Use a Map for storing arbitrary data instead. The Map reference contains a more detailed discussion of the pros & cons between plain objects and maps for storing key-value associations.

Typed Arrays present an array-like view of an underlying binary data buffer, and offer many methods that have similar semantics to the array counterparts. "Typed array" is an umbrella term for a range of data structures, including Int8Array, Float32Array, etc. Check the typed array page for more information. Typed arrays are often used in conjunction with ArrayBuffer and DataView.

Usually, to bind data to a DOM node, one could set properties directly on the object, or use data-* attributes. This has the downside that the data is available to any script running in the same context. Maps and WeakMaps make it easy to privately bind data to an object.

JSON (JavaScript Object Notation) is a lightweight data-interchange format, derived from JavaScript, but used by many programming languages. JSON builds universal data structures that can be transferred between different environments and even across languages. See JSON for more details.

With conventions, it is possible to represent any data structure in a string. This does not make it a good idea. For instance, with a separator, one could emulate a list (while a JavaScript array would be more suitable). Unfortunately, when the separator is used in one of the \"list\" elements, then, the list is broken. An escape character can be chosen, etc. All of this requires conventions and creates an unnecessary maintenance burden.

Typed Arrays present an array-like view of an underlying binary data buffer, and offer many methods that have similar semantics to the array counterparts. \"Typed array\" is an umbrella term for a range of data structures, including Int8Array, Float32Array, etc. Check the typed array page for more information. Typed arrays are often used in conjunction with ArrayBuffer and DataView.

Since jQuery 3, every two-character sequence of "-" (U+002D) followed by a lowercase ASCII letter in a key is replaced by the uppercase version of the letter, in alignment with the HTML dataset API. A statement like $( "body" ).data( { "my-name": "aValue" } ).data(); will return { myName: "aValue" }.

Calling .data() with no parameters returns a JavaScript object containing each stored value as a property. The object can be used directly to get data values (but note that property names originally containing dashes will have been modified as described below).

Since jQuery 1.4.3, data-* attributes are used to initialize jQuery data. An element's data-* attributes are retrieved the first time the data() method is invoked upon it, and then are no longer accessed or mutated (all values are stored internally by jQuery).

This has implications in how you can use them. For example, you can't (easily) have a script that creates JavaScript with an inline object. Suppose you wanted to write out this data as JSON with your script. It's as simple as writeFile('file', JSON.stringify(data)). There is no built-in library for creating JavaScript with JavaScript, so you couldn't write a JavaScript script with an object directly. At best, you could concatenate a static script (const menu = in your case) to the JSON-encoded data. 2351a5e196

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