Array | web.dev

array

is iterable
is not associated array.
inherits methods from Array.prototype, most of these methods are generic, they work correctly for any "array-like" object.

⚖️ array object properties vs. array elements

thery are separate❗
array's traversal and mutation operations cannot be applied to these named properties.

setting / accessing via anything other than nonnegative integers：

deleting an array element leaves a “hole” in the array and does not change the array’s length❗ (sparse array)

If an array literal contains multiple commas in a row, with no value between, the array is sparse.

🔸element
🔸element index
🔸array object property
🔰 creating arrays
- 🔢array literal
🔰 accessing elements
🔰 iterating elements
🔰 extending Array
- Array extension
other topics
- 🍄 array-like - object that has indexes and length.
- 🍄 sparse array - array that has "holes" in it.

🔰 accessing elements
- push() - append element.
- pop() - remove and return last element.
- unshift() - prepend element.
- shift() - remove and return first element.
combine elements
- join - 連接所有元素、合併成一個字串。
- reduce((result, element, index, array) => {...}) -
- reduceRight - reduce array from highest index to lowest. (from right to left)
find & search elements
- find - 回傳第一個符合條件的元素。否則回傳 undefined。
- findIndex - returns index of first matching element, -1 otherwise.
- includes - 判斷陣列是否包含特定元素。
- some - 測試陣列中是否有符合條件的元素。
- every - returns true if every element satisfies the condition.

( 🚧 to be removed ... )