JavaScript Basics (Arrays)

+ , Array

• Defining arrays

* Literal Way

var Array name = [Value,value,...]

* Constructor Function mode

var Array name = new Array (value,value,...) ; var Array name = new Array (length)

Create an object way to create an array analysis diagram

Attached: var num1 = 100; Number var num2 = new number (100); Object

var str1 = ' string '; string var str2 = new String (' string '); Object

var boo1 = true; boolean var Boo2 = new Boolean (true); Object

var arr1 = [1,2,3,4]; Object var arr2 = new Array (1,2,3,4); Object

Array classification

2 indexed arrays-arrays created by default

(1) Create an empty array (2) Create an indexed array based on an empty array

format: var Array name  = new Array (); Array name [ index value ] = value;

" index value is number (starting from 0)"

Note: When no value is stored in a specific location-undefined

2 Associative arrays-JavaScript-like objects

format: var Array name  = new Array (); Array name [ index value ] = value;" index value is string"

Note: The concept of associative arrays is not available in the ECMAScript official specification

Sparse array

Concept: The length of an array is greater than the number of elements in an array where the element has no value, the default undefined

The properties of the U array-length

Non-sparse array: The value of the length property = The current array contains the number of elements.

Sparse array: The value of the Length property > The current array contains the number of elements.

Eg:var arr2 = [];  ARR2[14] = ' a '; Console.log (arr2.length);//Output 15

Actions (Get/modify/delete)

2 getting the elements in an array: array name [ index value ]

2 modifying elements in an array: array name [ index value ] = new value

2 Deleting an element in an array : Delete array name [ index value ]

Note: Only the value at the corresponding location is deleted, but the position is reserved-undefined

U traversal Array

* for statement: Traversal array can control the start and end

* for.in statement: Only iterate through the array from start to finish

U Variables and Arrays

Analytic diagram of assignment operation of variables

An analytic diagram of an assignment operation for an array

U two-dimensional array

Concept: Nested structure traversal of arrays: for nested statements

L Common methods of operation

• Detection data type
• Conversion Method ToString ()
• In-and-out stacks-add/remove have an effect on the original array, delete returns the element added returns the length "

push () -Adds the last element to the array pop () -Deletes the last element in the array

Unshfit () -Adds an element to the beginning of the array shfit () -Deletes the first element in the array

• Sorting methods

reverse () -reverses the order of the elements in the array

Sort () -sorts the elements of an array

Note: The default sort is not sorted by small to large. If the number is two digits, it is arranged in the first digit.

Method: Use the array name. Sort () inside the constructor to change the default ordering so that it is ordered sequentially.

Eg:arr.sort (function (b) {

return a < b;  ------< from large to small; > From small to large

});

• Interception method:

2 Slice (start,end) "Note: There is no effect on the original array"

The start---Indicates which index value from the array begins to intercept; end---By default, indicates the end of the array

Set Value: Represents the previous return value intercepted to the current index value: The result of the interception

var arr1 = Arr.slice (1,3); Console.log (ARR,ARR1);

2 Splice (index, Howmany, Element1,element2,... elementn) "NOTE: default is an array"

Index---represents the indexed value of the current array (where it was deleted or added)

Howmany---Indicates the number of deleted elements (if 0, does not delete) Element1---represents the added element

* Note-is added to the index position of the array; return value-represents the currently deleted element

• Search Content--Location

2 indexOf (Element)

Element-represents the content of elements searched in an array

Usage: Starts the search from the index value of 0 in the array, then backwards; return value: The index value of the first matched element

Note: If the searched element does not exist in the array, 1 is returned

2 lastIndexOf (Element)

Element-represents the content of elements searched in an array

Usage: Return value: The index value of the last matching element

JavaScript Basics (Arrays)