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:
const myArray = [1, "hello", true, null];
- Use Array constructor:
const anotherArray = new Array(5); // 創(chuàng)建一個(gè)包含5個(gè)空槽的數(shù)組 const yetAnotherArray = new Array(1, 2, 3);
Access array elements:
Use square bracket notation and indexing:
const fruits = ["apple", "banana", "orange"]; console.log(fruits[0]); // 輸出： "apple" (第一個(gè)元素) console.log(fruits[2]); // 輸出： "orange" (第三個(gè)元素)
Modify array elements:
Assign the new value to the desired index:
fruits[1] = "grape"; console.log(fruits); // 輸出： ["apple", "grape", "orange"]
Commonly used array methods:
- push(): Add one or more elements to the end of the array.
fruits.push("mango");
- pop(): Removes the last element of the array and returns it.
const removedFruit = fruits.pop();
- unshift(): Adds one or more elements to the beginning of the array.
fruits.unshift("kiwi");
- shift(): Deletes the first element of the array and returns it.
const firstFruit = fruits.shift();
- slice(): Creates a shallow copy of a portion of the array.
const citrusFruits = fruits.slice(1, 3); // 從索引1到2（不包括2）的元素
- splice(): Add/remove array elements at the specified position.
fruits.splice(1, 0, "pear"); // 在索引1處插入"pear" fruits.splice(2, 1); // 從索引2處刪除1個(gè)元素
- concat(): Creates a new array by concatenating existing arrays.
const combinedFruits = fruits.concat(["pineapple", "strawberry"]);
- join(): Concatenates all array elements into a string, separated by the specified delimiter.
const fruitString = fruits.join(", ");
- indexOf(): Returns the first index of the given element.
const index = fruits.indexOf("apple");
- includes(): Checks whether the array contains an element.
const hasBanana = fruits.includes("banana");
- forEach(): Execute the provided function once for each array element.
fruits.forEach(fruit => console.log(fruit));
- map(): Creates a new array by applying a function to each element of the original array.
const fruitLengths = fruits.map(fruit => fruit.length);
- filter(): Creates a new array containing only elements that pass the test provided by the function.
const longFruits = fruits.filter(fruit => fruit.length > 5);
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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