Nine console commands to make JS debugging easier

Last Update:2016-08-21 Source: Internet

Author: User

Tags assert

Developer on Alibaba Coud: Build your first app with APIs, SDKs, and tutorials on the Alibaba Cloud. Read more ＞

I. Commands to display information

   1: <!DOCTYPE html>   2:

The most common is the console.log.

Two: Placeholder
Console The above concentration supports printf placeholder format, supported placeholders are: characters (%s), integers (%d or%i), floating-point numbers (%f), and objects (%o)
   1: <script type="text/javascript">   2:         console.log("%d年%d月%d日",2011,3,26);   3: </script>
Effect:
Iii. Grouping of information   1: <!DOCTYPE html>   2: 
Effect:
Iv. Viewing the information of an object
Console.dir () can display all properties and methods of an object.
   1: <script type="text/javascript">   2:         var info = {   3:             blog:"http://www.ido321.com",   4:             QQGroup:259280570,   5:             message:"程序爱好者欢迎你的加入"   6:         };   7:         console.dir(info);   8: </script>
Effect:
V. Display the contents of a node
Console.dirxml () is used to display the Html/xml code contained in a node of a Web page.
   1: <!DOCTYPE html>   2: 
Effect:
Vi. Judging if the variable is true
Console.assert () is used to determine whether an expression or variable is true. If the result is no, a corresponding message is output in the console and an exception is thrown.
   1: <script type="text/javascript">   2:     　　var result = 1;   3:     　　console.assert( result );   4:     　　var year = 2014;   5:     　　console.assert(year == 2018 );   6: </script>
1 is a value of 0, is true, and the second is false, displaying an error message on the console
Tracing the call trajectory of the function.
Console.trace () is used to track the call path of a function.
   1: <script type="text/javascript">   2: /*函数是如何被调用的，在其中加入console.trace()方法就可以了*/   3: 　　function add(a,b){   4:         console.trace();   5: 　　　　return a+b;   6: 　　}   7: 　　var x = add3(1,1);   8: 　　function add3(a,b){return add2(a,b);}   9: 　　function add2(a,b){return add1(a,b);}  10: 　　function add1(a,b){return add(a,b);}  11: </script>
Console output Information:
Eight, chronograph function
Console.time () and Console.timeend () are used to display the elapsed time of the code.
   1: <script type="text/javascript">   2: 　　console.time("控制台计时器一");   3: 　　for(var i=0;i<1000;i++){   4: 　　　　for(var j=0;j<1000;j++){}   5: 　　}   6: 　　console.timeEnd("控制台计时器一");   7: </script>
Run Time is 38.84ms
Performance analysis of Console.profile ()
Performance analysis (Profiler) is the analysis of the various parts of the running time, to find out the bottleneck, the method used is Console.profile ().
   1: <script type="text/javascript">   2:     　　function All(){   3:             alert(11);   4: 　　　　     for(var i=0;i<10;i++){   5:                 funcA(1000);   6:              }   7: 　　　　    funcB(10000);   8: 　　    }   9:  10:     　　function funcA(count){  11:     　　　　for(var i=0;i<count;i++){}  12:     　　}  13:  14:     　　function funcB(count){  15:     　　　　for(var i=0;i<count;i++){}  16:     　　}  17:  18:     　　console.profile(‘性能分析器‘);  19:     　　All();  20:     　　console.profileEnd();  21:     </script>
Output
Nine console commands to make JS debugging easier

This article is an English version of an article which is originally in the Chinese language on aliyun.com and is provided for information purposes only. This website makes no representation or warranty of any kind, either expressed or implied, as to the accuracy, completeness ownership or reliability of the article or any translations thereof. If you have any concerns or complaints relating to the article, please send an email, providing a detailed description of the concern or complaint, to info-contact@alibabacloud.com. A staff member will contact you within 5 working days. Once verified, infringing content will be removed immediately.

A Free Trial That Lets You Build Big!

Start building with 50+ products and up to 12 months usage for Elastic Compute Service

Get Started for Free

Sales Support

1 on 1 presale consultation

Chat Contact Sales
After-Sales Support

24/7 Technical Support 6 Free Tickets per Quarter Faster Response

Open a Ticket
Alibaba Cloud offers highly flexible support services tailored to meet your exact needs.

Learn More