📘Array

🚧 under construction

JS ⟩ value ⟩ object⟩ built-in ⟩ Array

(Object)

• an ordered collection of values.

• each value is called an element.

• each element has a numeric position in the array, known as its index.

JavaScript arrays are untyped:

• an array element may be of any type.

• different elements of the same array may be of different types.

🧨

arrays are iterated "live"❗️

⭐️

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：

• will not set / retrieve an array element

• will set / access one of the array's object properties.

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.

👥

• NodeList vs. Array

• Array is iterable.

• bracket notation [] is used to access element.

📗

• JavaScript: The Definitive Guide > Ch. 7 Arrays

📘

• Guides ⟩ Arrays ⭐️
• Array ⟩

  • array elements cannot be accessed using arbitrary strings as indexes

✨

• codepen ⟩ Array: intersection, union, difference ...
• randomPassword()
• randomInt()

📍

( 🚧 to be removed ... )

• matrix methods (instance):

  • mat.transpose() - see matrix in "columns"

  • mat.matrixMap()

  • mat.maxElementInEachColumn() - for number matrices only.

🗣

• How to get first N number of elements from an array

• Remove empty elements from an array