Arrays are the most common data structures in the computer programming world. Any programming language contains arrays. It is a built-in model in a programming language that is usually very efficient and can be used to store data for different needs.

Arrays in JavaScript

The standard definition of an array is a linear collection of elements that can be accessed by an index, usually a number, to calculate the offset between the locations in which the elements are stored.

Whereas arrays in JavaScript, strictly speaking, should be called objects, are a special kind of object, and the indexes are its properties, which can be integers, but because the property names of objects in JavaScript must be strings, these indexes are internally converted from numeric to string types.

Use arrays

2.1 Creating and initializing arrays

You can declare an array variable with the [] operator:

var nums = [];     // Length is 0
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Of course, you can also declare an array by simply putting elements in it:

var nums = [1.2.3.4];    // Length 4
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Alternatively, you can create it using the constructor:

var nums = new Array(1.2.3.4.5);
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Similarly, you can use it to create an array of length 10 with zero elements:

var arr = new Array(10).fill(0);
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Finally, we can determine whether an object is an Array by using array.isarray () :

var a = 1;
console.log(Array.isArray(a)); // false
console.log(Array.isArray(nums)); // true
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2.2 Adding and removing elements

Add elements:

  1. pushMethod: add the element to the end of the array;
  2. unshiftMethod: Insert an element at the beginning of an array.

Delete element:

  1. popMethod: Remove an element from the end of an array.
  2. shiftMethod: Delete the first element of an array.
  3. sliceMethod: Remove elements for the appropriate location and number. You can also add or replace elements with a third argument.

Tips!!! :

  1. In JavaScript, an array is an object that can be modified. Add elements, and it grows dynamically;
  2. throughpush 和 popMethod, you can use an array to simulate a stack;
  3. throughunshift 和 shiftMethod, you can use arrays to simulate queues.

2.3 Two-dimensional and multidimensional arrays

JavaScript only supports one-dimensional arrays, but you can implement any multidimensional array by nested arrays:

var arrs = [[1.2], [3.4]]
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2.4 JavaScript array methods

The method name describe
concat Concatenate two or more arrays and return the result
every Runs the specified function for each element in the array, returning true if the function returns true for each item
filter Runs the specified function for each element in the array, returning an array of items for which the function returns true
forEach Runs the specified function for each element in the array, returning no value
join Concatenate all array elements into a single string
indexOf Returns the index of the first array element equal to the given argument, or -1 if not found
lastIndexOf Returns the largest index value found in the array for elements equal to the given parameter
map Runs the specified function for each item in the array, returning an array of the results of each function call
reverse Flip the array
slice Pass in the index value and return the elements in the array as the new array
some Run the specified function for each item in the array. Return true if any item returns true
sort Sort the elements of an array
toString Returns the array as a string
valueOf Similar to the toString