08.18 JavaScript 06 array array concept create array read elements in array sparse array add and remove array elements array iterate over array of multidimensional array methods class array object as an array of strings

# array
The Concept of # # # array
* Array is an ordered set of values
* Each value in the array is called an element
* Each element can be a value of any data type
* Each element has an index (subscript)
* The index of the element starts at 0 and increments in order. The element's largest index 2^32-2

# # # Create an array
* Direct Volume ' [] '
* Constructor Method ' new Array () '

# # # Read and write elements in an array
* array name [index]


# # # Sparse Array
* The index of the JS array is continuous
* There is no continuous assignment to the element, and the element with no assignment is automatically assigned to the value undefined

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# # # Add and remove elements of an array
*  add an array element
    *   Specify an index to add an element
    *   The array length as the index of the new element    "Arr[arr.length ] = value '
    *   at the end of the array add element push ()    " Arr.push () '
    *   add element before array unshift ()    ' Arr.unshift () '
    *   add elements anywhere in a number array    Splice (index, 0, value)   

 

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*  delete elements of an array
    *    change the Length property of the array    ' arr.length-= 1;  arr.length-= 2 '
    *   Delete The most subsequent element   pop ()
    *   Deletes the first element of an array   shift ()
    *   deletes the specified number of elements at the specified position    splice ( index, length)

# # # Array traversal
* For Loop
* For in

 

Span style= "COLOR: #b22222" >### multidimensional array

### Array method
* join ([spacer symbol])     stitch Each element of an array into a string     return string
Span style= "COLOR: #808080" >* slice (start, end)     intercept part of the array, returning a new array
* concat (arr, arr ....)     merging arrays. Returns a new array
* tostring ()     converts an array to a string
* reverse ()    flip array side effects
* sort ()      sort    Side effects
* push () Pop ()    side effects
* shift ()   unshift ()    side effects

 

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### class Array Object
*  arguments
* elementcollection     elements  
&NBSP;&NBSP;&NBSP;&NBSP;&NBSP;&NBSP;&NBSP;&NBSP;
          document.getElementsByTagName ()
          element.getelementsbytagname ()

 

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### the string as an array
Span style= "COLOR: #808080" The >*  string has a partial array attribute
*  string also has the length property to get the lengths of the string
. Span style= "COLOR: #808080" >*  can also remove a character from a string by [index value]

08.18 JavaScript 06 array array concept create array read elements in array sparse array add and delete array of elements array traversal method class array array object as array string