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1. Introduction

1.1 description

An array is an ordered collection of values. Each value is called an element, and each element has a position in the array, represented by a number, called an index. JavaScript arrays are untyped: array elements can be of any type, and different elements in the same array may have different types. JavaScript authoritative Guide (sixth Edition)

1.2 definition method

Var names=new Array ("Zhang San", "Li Si", "Wang Wu")

/ / or

Var names= [Zhang San, Li Si, Wang Wu]

1.3 Properties

Length: represents the length of elements in an array.

two。 Example method commonly used methods:

1) unshift (): insert an element in the head of the array

2) shift (): removes and returns the first element of the array

3) push (): insert elements at the end of the array

4) pop (): removes and returns the last element of the array

2.1 concat (): join elements into an array. The original array will not be modified and a new array will be returned.

Parameters:

① value1,value2.valueN: any number of valu

Return value:

{Array} A new array containing the original Array and newly added elements.

Example:

Var demoArray= ['await,' baked,'c']

Var demoArray2=demoArray.concat ('e')

Console.log (demoArray); / / = > demoArray: the original array does not change.

Console.log (demoArray2); / / = > ['axiomagy, pageantry, pageantry, cinnamon,']

2.2 every (): iterate through the elements in turn to determine whether each element is true

Parameters:

① function (value,index,self) {}: each element uses this function to determine whether it is true or not, and when one is judged to be false, the traversal ends immediately.

Value: elements that the array traverses

Index: element serial number

Self: Array itself

Return value:

{Boolean}: true; is returned only if each element is true. As long as one is false, false is returned.

Example:

Var demoArray= [1, 2, 3]

Var rs=demoArray.every (function (value, index, self) {

Return value > 0

})

Console.log (rs); / / = > true

2.3 filter (): iterates through the elements in turn, returning a new array containing eligible elements

Parameters:

① function (value,index,self) {}: each element calls this function in turn, returning a new array containing eligible elements.

Value: elements that the array traverses

Index: element serial number

Self: Array itself

Return value:

{Array} A new array containing eligible elements

Example:

Var demoArray= [1, 2, 3]

Var rs=demoArray.filter (function (value, index, self) {

Return value > 0

})

Console.log (rs); / / = > [1,2,3]

2.4 forEach (): iterates through the elements in turn, executing the specified function; no return value

Parameters:

① function (value,index,self) {}: this function is called by each element in turn

Value: elements that the array traverses

Index: element serial number

Self: Array itself

Return value: none

Example:

Var demoArray= [1, 2, 3]

DemoArray.forEach (function (value, index, self) {

Console.log (value); / / = > output: 1 2 3

})

IndexOf (): looks for matching elements in the array. If there is no matching element,-1 is returned. Use the "= =" operator when looking up, so distinguish between 1 and'1'

Parameters:

① value: the value to look for in the array.

② start: the location of the sequence number to start the search, or 0. 0 if omitted.

Return value:

{Int}: returns the sequence number of the first matching value in the array, or-1 if it does not exist

Example:

['await,' baked,'c'] .indexOf ('a'); / / = > 0

['averse,' baked,'c'] .indexOf ('averse, 1); / / = >-1

['await,' baked,'c'] .indexOf ('d'); / / = >-1

[1, 2, 3] .indexOf ('1'); / / = >-1: the'= = 'matching method adopted

2.6 join (): splices all elements in the array into a string with a delimiter

Parameters:

① sparator {String}: the delimiter between elements, if omitted, is separated by default because of the English comma','.

Return value:

{String}: a string of elements spliced with sparator as a delimiter.

Example:

['averse,' baked,'c'] .join (); / / = > 'arecalogical brecedence c'

['await,' baked,'c'] .join ('-'); / / = > 'amurbmurc'

2.7lastIndexOf: reverse look for matching elements in the array. If there is no matching element,-1 is returned. Use the "= =" operator when looking up, so distinguish between 1 and'1'

Parameters:

① value: the value to look for in the array.

② start: the location of the sequence number to start the search. If omitted, the search starts with the last element.

Return value:

{Int}: start from right to left to find the sequence number of the first matching value in the array. If it does not exist, return-1

Example:

['averse,' baked,'c'] .lastIndexOf ('a'); / / = > 0

['averse,' baked,'c'] .lastIndexOf ('averse, 1); / / = > 0

['averse,' baked,'c'] .lastIndexOf ('d'); / / = >-1

[1, 2, 3] .lastIndexOf ('1'); / / = >-1: the'= = 'matching method adopted

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