Explanation on Arrays and Arrays method

Detailed explanation and common methods of JavaScript arrays:

What is an array?

In JavaScript, an array is a special object used to store a series of values ​​(elements) under a variable name. The values ​​can be of different data types (numbers, strings, booleans, objects, or even other arrays).

Main features:

• Ordered: The elements in the array have a specific order, with their positions indexed starting from 0.
• Mutable: Once an array is created, its elements can be changed.
• Dynamic: Arrays can grow or shrink in size as needed.

Create array:

• Literal representation:

<code class="language-javascript">   const myArray = [1, "hello", true, null]; </code>

• Use Array constructor:

<code class="language-javascript">   const anotherArray = new Array(5); // 创建一个包含5个空槽的数组
   const yetAnotherArray = new Array(1, 2, 3); </code>

Access array elements:

Use square bracket notation and indexing:

<code class="language-javascript">   const fruits = ["apple", "banana", "orange"];
   console.log(fruits[0]); // 输出： "apple" (第一个元素)
   console.log(fruits[2]); // 输出： "orange" (第三个元素)</code>

Modify array elements:

Assign the new value to the desired index:

<code class="language-javascript">   fruits[1] = "grape"; 
   console.log(fruits); // 输出： ["apple", "grape", "orange"]</code>

Commonly used array methods:

• push(): Add one or more elements to the end of the array.

<code class="language-javascript">   fruits.push("mango"); </code>

• pop(): Removes the last element of the array and returns it.

<code class="language-javascript">   const removedFruit = fruits.pop(); </code>

• unshift(): Adds one or more elements to the beginning of the array.

<code class="language-javascript">   fruits.unshift("kiwi"); </code>

• shift(): Deletes the first element of the array and returns it.

<code class="language-javascript">   const firstFruit = fruits.shift(); </code>

• slice(): Creates a shallow copy of a portion of the array.

<code class="language-javascript">   const citrusFruits = fruits.slice(1, 3); // 从索引1到2（不包括2）的元素</code>

• splice(): Add/remove array elements at the specified position.

<code class="language-javascript">   fruits.splice(1, 0, "pear"); // 在索引1处插入"pear"
   fruits.splice(2, 1); // 从索引2处删除1个元素</code>

• concat(): Creates a new array by concatenating existing arrays.

<code class="language-javascript">   const combinedFruits = fruits.concat(["pineapple", "strawberry"]); </code>

• join(): Concatenates all array elements into a string, separated by the specified delimiter.

<code class="language-javascript">   const fruitString = fruits.join(", "); </code>

• indexOf(): Returns the first index of the given element.

<code class="language-javascript">   const index = fruits.indexOf("apple"); </code>

• includes(): Checks whether the array contains an element.

<code class="language-javascript">   const hasBanana = fruits.includes("banana"); </code>

• forEach(): Execute the provided function once for each array element.

<code class="language-javascript">   fruits.forEach(fruit => console.log(fruit)); </code>

• map(): Creates a new array by applying a function to each element of the original array.

<code class="language-javascript">   const fruitLengths = fruits.map(fruit => fruit.length); </code>

• filter(): Creates a new array containing only elements that pass the test provided by the function.

<code class="language-javascript">   const longFruits = fruits.filter(fruit => fruit.length > 5); </code>

This is a basic overview of JavaScript arrays and their methods. There are many other methods available, each with its own specific purpose. Hope this helps!

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