An extension of an array in ES6

The Array.from () method is used to convert two types of objects into real arrays: arrays-like objects and objects that can be traversed.

PHP has a kind of return JSON grow: let arr1={0: ' 1 ', 1: ' A ', 2: ' C '}; ES6 can be written directly to let Arr2=array.from (arr1);//[' 1 ', ' A ', ' C ']. ES5 can be written as Var arr3=[].slice.call (ARR1); Thank you ES6.

As long as the data structure of the iterator interface is deployed, Array.from can convert it to an array. Array.from (' hello ')//[h,e,l,l,o]; If the argument is a real array, Array.from will return an identical new array.

The Array.from method also supports array-like objects. The so-called array-like object, the intrinsic feature is only one point, that is, the length property must be. Therefore, any object with the Length property can be converted to an array by means of the Array.from method, which cannot be converted by the extension operator.

Array.from can also accept the second parameter, which acts like a map method of an array, which is used to process each element and put the processed value into the returned array. Array.from ([=>x*x), (x)//[1,4,9]

Use Array.from to replace a member with a Boolean value of false. Array.from ([1,,2,,3], (n) =>n| | 0)//[1,0,2,0,3]

This can be used as a filter. I say why the applet, react does not provide the basic function of filter.

Array.from () can convert various values to real arrays and provide map functionality. As long as there is a raw data structure, it can be processed first, and then into the canonical array structure, so that a large number of array methods can be used.

Array.from () can convert a string to an array and then return the length of the string. Because it handles Unicode characters correctly, you can avoid the bug that JS will count Unicode characters greater than \ufff as 2 characters.

function Countsymbols (String) {  return  array.from (string). length;

The Array.of () method is used to convert a set of values to an array. The main purpose of this method is to compensate for the insufficiency of the array constructor function array (). The difference in the number of parameters causes the behavior of the array to be different. Array () returns a new array consisting of parameters only if the number of arguments is not less than 2. When the number of parameters is only 1, it is actually the length of the specified array.

Array.of can basically be used to replace array () or new array (), and there are no overloads due to different parameters. Its behavior is very uniform.

Array.of always returns an array of parameter values. If there are no arguments, an empty array is returned.

　　

The Find method of an array instance that is used to find the first qualifying array member. Its argument is a callback function, in which all array members execute the callback function sequentially until they find the first member to return a value of true, and then return the member. If there are no eligible members, the undefined is returned;

The callback function of the Find method can accept 3 parameters, in turn, the current value, the current position, and the original array.

The FindIndex method of an array instance is used very similarly to the Find method, returning the position of the first qualifying array member, or 1 if none of the conditions are met.

The Fill method of an array instance populates the array with the given values.

ES6 provides 3 new methods-entries (), keys (), and values () to iterate through the array. They all return a Walker object. You can use for. of loop traversal, keys () is the traversal of the key name, and values () is the traversal of the key value, and enteries () is the traversal of the key-value pair.

The Array.proptotype.includes method returns a Boolean value that indicates whether a number group contains the given value, similar to the includes method of the string.

There is no value for a position of the array's empty exponent group.

Not all.

An extension of an array in ES6