ES6 array method

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Array Array

In order to supplement some defects of some methods in the original array ,ES6 Add a lot more in the array API Such as Array.from include fill wait .

Array.from()

 The API  It can be used to convert class arrays and convenient objects to arrays , such as  function  Medium arguments  object （ An array of class ）,set map es6 New traversable objects 

function test () { 
   
    var arr = Array.from(arguments);
    console.log(arr);
}
test(1,2,3); // [1,2,3]

 For browsers that are not yet compatible with this method, you can use slice  Instead of 
[].slice.call(obj) //  The same result will be returned 

TIP 
 This function can also accept the second parameter , Be similar to map Method   For each element 
Array.from(obj,(i) => i*i) // For each element squared 

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Array,of()

 Used to convert a set of numbers into an array 
var arr = Array.of(1,2,3,4) // [1,2,3,4]

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Of the array instance find And findIndex

find  Method is used to find the first qualified on the array   value , And return it 
 such as  [1,2,5,6,2,4];
 We want to find the first... On this array   value   Greater than  5  Number of numbers 
[1,2,5,6,2,4].find((item) => item > 5) // 6
 If you find the last value that does not meet the condition   So return  undefined

findIndex  Used to return the subscript of the first value in the array that satisfies the condition 
[1,2,5,6,2,4].find((item) => item > 5) // 3
 If you find the last one that doesn't meet the conditions , Then the return    -1

 And very important , These two functions can actually  NaN  了 
[NaN].find((item) => Object.is(NaN,item)) // NaN

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Array instance fill

fill(item,start,end)
 Give a value , Use this value to fill the entire array , This function can also take two arguments , A starting position , An end position 
 When you use this function to fill in , When only the first parameter is given , Will directly fill the entire array , Whether or not there is a value at a certain position 

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Of the array instance entries keys values

entries => [key,value]
keys => key  Subscript 
values => value   value 

for(let [index,value] of arr.entries()){ 
   
    console.log(index,value)
}

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Of the array instance includes

 Used to detect whether an array contains a value   And back to   One bool value 
include(item,st=0)
 The first parameter is the value used to detect 
 The second parameter is the starting position of the probe   The default is 0 Start 

 If the browser does not support this method , It can also be used.  some Method   Instead of 

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Array derivation ES7

var a1 = [1,2,3,4]
var a2 = [for (i of a1) i*2] // [2,4,6,8]

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