API class List

The Unpoly documentation uses the term List to refer to an array-like value.

There is no actual List class. Instead that term refers to an abstract interface for objects that have a { length } property and allow random access to an indexed element:

list[2] // => 'hello'
list.length // => 10

You can also use them in a for loop:

for (let element of list) {
  console.log(element)
}

Whether a list supports additional utilities like forEach() or map() depends on the specific type of the list value.

Common list types

Common types of array-like values include:

• Array
• NodeList
• HTMLCollection
• arguments object
• jQuery object

Converting lists to arrays

Sometimes we want to convert an array-like value into an actual Array so we can call methods like map() or flat().

One way to do this is to destructure the array-like value:

let array = [...list]

One drawback of destructuring is that it will always create a new array, even if the given list is already an Array. To only convert non-Array values, use up.util.toArray():

let array = up.util.toArray()