JS, entries(), keys(), values(), some(), object Assign() traversal array usage

js in entries(),keys(),values() , some(), Object.assign() Traversal array usage

ES6 Provides entries(),keys(),values() Method returns the iterator of the array , For traversers （Iterator） have access to for…of Facilitate , It can also be used entries（） The returned iterator Iterator.next() Method .

1. Use keys() Traverse .
keys() Returns the iterator of the index number of the array element .

const arr1 = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k']
for (let index of arr1.keys()) {
  console.log(index);
}

result ：
You can see that the output is the of each array element index.

0  
1  
2  
3  
4  
5  
6  
7  
8  
9  
10 

2. Use values() Traverse .
values() The return is the traversal of the array element value .

for (let val of  arr1.values()) {
  console.log(val);
}

result ：

a 
b 
c 
d 
e 
f 
g 
h 
i 
j 
k 

3. Use entries() Traverse .
Use with deconstruction , You can get the element index and value.

for (let [index, val] of arr1.entries()) {
  console.log(index, val);
}

result ：

0 'a'
1 'b'
2 'c'
3 'd'
4 'e'
5 'f'
6 'g'
7 'h'
8 'i'
9 'j'
10 'k'

4. Use Iterator.next() Traverse .
be based on entries() The returned iterator , To call the traverser next() The method can get the access entry of each element , The entrance has a done Attribute can indicate whether it is convenient to end . You can get... Through the entrance value attribute , It is the index of the element and the array of values .

let arrEntries=arr1.entries();
let entry=arrEntries.next();
while(!entry.done){
  console.log(entry.value);
  entry=arrEntries.next();
}

5.some Method
Used to detect whether the elements in the array meet the specified conditions （ Function provides ）. Each element of the array will be executed in turn ： If I have one element that satisfies this condition , Then the expression returns true , The remaining elements are no longer checked .
Be careful ： some() Empty arrays are not detected .
Be careful ： some() It doesn't change the original array .

array.some(function(currentValue,index,arr),thisValue)

Parameter description ：
Parameters 1：function(currentValue, index,arr)
must . function , Every element in the array performs this function .
Function parameter ：
(1)currentValue must . The value of the current element
(2)index Optional . The index value of the current element
(3)arr Optional . The array object to which the current element belongs
Parameters 2：thisValue
Optional . Object as the callback to execute , Pass to function , Used as a “this” Value .
If you omit thisValue ,“this” The value of is “undefined”

var age=[12,42,34,10];

      aa(){
        var a=this.age.some((x)=>{
          return x>100;
        });
        console.log(a);// The result is false
      }

6. The two objects are the same key assignment

row.row The value inside is assigned to this.form Inside 
Object.keys(this.form).forEach(key => {
        this.form[key] = row.row[key];
      });