Functions and array traps in ES6

function Deconstruction of objects

When we detach from the front and back, the backend often returns JSON-formatted data, and the good intentions of the front end is to pass the JSON format data directly to the inside of the function as a parameter. ES6 provides us with such an assignment of deconstruction.

Let JSON = {    A:' xzblogs ',    B:' Little Smart '}function Fun ({a,b= ' if no B with this substitute '}) {    Console.log (A, b);} Fun (JSON);

is not the feeling of convenience a lot, we no longer have to pass the parameters.

function Deconstruction of arrays

The function can deconstruct the JSON, and that's a much better solution to our array, let's look at the code below. We declare an array, then write a method, and finally use ... To perform the deconstruction assignment.

Let arr = [' xzblogs ', ' Little Wise ', ' Zachary ']; function Fun (a,b,c) {    console.log (a,b,c);} Fun (... arr.);

In usage

In is used to determine whether a value exists in an object or array. Let's take a look at how to tell if there is a value in the object.

Object judgment

Let obj={    A:' xzblogs ',    B:' Little Wise '}console.log ( in obj);  // true

Array judgment

Let's take a look at the drawbacks of ES5 judgment, which used to be judged by the length property, which means that there is no array element for 0. But that's not accurate, or there are drawbacks in real-world development.

Let arr=//5 above the code output 5, but the array is actually all empty values, this is a pit ah. That will solve the problem with ES6 in.

Let arr=[,,,,,];console.log (in//false let arr1=[' xz ', ' Little Wise '); Console.log ( in arr1);  // true Note: The 0 here refers to whether the array subscript position is empty.

Array Traversal method 1.forEach

Let arr=[' xzblogs ', ' Little Wisdom ', ' Zachary '];arr.foreach ((val,index)=Console.log (index,val)); The feature of the Foreach loop is that it is automatically omitted as an empty array element, which is equivalent to simply sifting us out of space. Sometimes it can be a disservice to us. 

2.filter

Let arr=[' xzblogs ', ' Little Wisdom ', ' Zachary '];arr.filter (x=console.log (x)); This approach I've told in Vue, he actually has a looping function, Here we are reviewing again. 

3.some

Let arr=[' xzblogs ', ' Little Wise ', ' Zachary '];arr.some (x=>console.log (x));

4.map

Let arr=[' xzblogs ', ' Little Wise ', ' Zachary '];console.log (arr.map (x= ' web ')); Map is a replacement here, and this is a follow-up course that will be explained in detail. 

Array conversion string

In development we often encounter the output of the array into a string form, we learn two methods today, you should pay attention to the difference between the two methods.

Join () method

Let arr=[' xzblogs ', ' Little Wisdom ', ' Zachary '];console.log (arr.join (' | ') ) ; the join () method is to add some spacing between the elements of the array, which is useful in development. 

toString () method

Let arr=[' xzblogs ', ' Little Wise ', ' Zachary '];console.log (arr.tostring ()); The conversion is only separated by commas. 

Functions and array traps in ES6