Summary of common JavaScript Array methods and javascript Array

Summary of common JavaScript Array methods and javascript Array

In JavaScript, We need to operate arrays from time to time. The common methods are summarized as follows:

1. Add data

Adding data to arrays in JavaScript is mainly divided into two methods.

Add content from the end of the array: push method

Add content from the front end of the array: unshift Method

The returned values of these two methods are the length of the array.

Var arr = [1, 2, 3]; // Add arr from the end. push (4); console. log (arr); // [1, 2, 4] // Add arr from the front end. unshift (0); console. log (arr); // [0, 1, 2, 3, 4]

2. delete data

Like adding data, you can delete data in two ways.

Add content from the end of the array: pop Method

Add content from the front end of the array: shift Method

The returned values of both methods are deleted data.

Var arr = [1, 2, 3]; // Delete arr from the end. pop (); console. log (arr); // [1, 2] // Delete arr from the front end. unshift (); console. log (arr); // [2]

3. Delete and add data from a specified location

Splice (startIndex, deleteCount, addValue1, addvalue2 ...): delete deleteCount data starting from the startIndex position of the array, and insert addValue1, addValue2, etc. The returned value is an array composed of the deleted array.

var arr=[1,2,3,4,5]; var deleteArr=arr.splice(1,2,8,9);  console.log(deleteArr);//[2,3] console.log(arr);//[1,8,9,4,5] 

As we know above, the array deletion method returns the deleted content, and the added method returns the length after the array is changed.

4. Reverse Order Array

Reverse (): sorts the array content in reverse order.

var arr=[1,2,3]; arr.reverse(); console.log(arr);//[3,2,1] 

5. Combine the array content into a string with a specific Separator

Join (seperator): A string consisting of the array content separated by seperator

var arr=[1,2,3]; arr.join(','); console.log(arr);//1,2,3 

6. merge two Arrays

Concat (): merges the array and returns a new array without affecting the original array.

var arr1=[1,2,3]; var arr2=[4,5,6];  var newArr=arr1.concat(arr2);  console.log(arr1);//[1,2,3] console.log(arr2);//[4,5,6] console.log(newArr);//[1,2,3,4,5,6] 

7. array sorting

Sort (): by default, the array is sorted in ascending order by numbers or letters, but you can also customize the descending order.

Var arr = [3, 5, 1]; arr. sort (); console. log (arr); // [, 5]; // specify the descending order var arr1 = [, 7]; arr1.sort (function (a, B) {return B-a;}) console. log (arr1); // [7, 4, 2]

8. truncate sub-array

Slice (startIndex, endIndex): intercept the content from startIndex to endIndex in the array, excluding the content of the endIndex location to form a new array

var arr=[1,2,3,4,5,6];  var newArr=arr.slice(1,3);  console.log(arr);//[1,2,3,4,5,6] console.log(newArr);//[2,3] 

9. determine the position of the given data in the array

IndexOf (data): This method returns the location of the first element in the array where data is located. If no value is found,-1 is returned.

var arr=[1,2,3];  var loc=arr.indexOf(1); console.log(loc);//0  var newLoc=arr.indexOf(4); console.log(newLoc);//-1 

10. iterator

Arrays have many iterator methods.

A. Normal traversal array: forEach (function (value, index, arr) {}), where index is index, value is value, and arr is the array itself

Var arr = [, 3]; // index is the index and value is the value arr. forEach (function (value, index, arr) {console. log (''index:" + index + "" + "value:" + value )})

B. filter Array: filter (): filters the Array Based on the filter conditions, but does not change the original array.

Var arr = [1, 2, 3, 4]; // return the content larger than 2 in the array var newArr = arr. filter (function (item) {return item> 2;}) console. log (arr); // [1, 2, 3, 4] console. log (newArr); // [3, 4]

C. ing array: map (). After each element of the array is mapped, a new array is returned without changing the original array.

Var arr = [1, 2, 4]; // doubles each value of the array var newArr = arr. map (function (item) {return item * 2;}); console. log (arr); // [1, 2, 3, 4] console. log (newArr); // [2, 4, 6, 8]

The above is all the content of this article. I hope it will be helpful for your learning and support for helping customers.