node. JS Debugging

With a few days of node. js feel very novel, but debugging problem is really worry people, the beginning of lazy learning debugging method, look at the abnormal content can be, but with the code complexity of the rise, not all errors are grammatical errors, do not debug, have to search information, learn how to debug.

No supervisor to restart the service every time

The students who have used PHP must be aware that when a script file is modified, the new content is loaded as soon as the page server is refreshed. But node. js in the first reference to a file after parsing will put it into memory, the next time access to directly in memory to improve efficiency, but this is a problem for our development, modified a module can only restart after the server to take effect, debugging efficiency is still very low.

As a result, node. JS has the Supervisor plugin to help us make solid file changes, automatically restart the server, Supervisor is a node. js package, installation is simple, using NPM installation commands can be, because we need to run in the console, so we need to install in the global environment

NPM install-g Supervisor

So we can use Supervisor to start the script.

Supervisor Index

When we make changes to the file, we can see that the console has more than three lines, the server has been restarted

Native Console debugging

node. js natively supports debugging, and adding a breakpoint before the statement is preceded by a debugger instruction

var server=require ('./server '),    router=require ('./router '),    requesthandlers=require ('./requesthandlers ') );d Ebugger;var handle={};d ebugger;handle['/']=handle['/start ']=requesthandlers.start;debugger;handle['/upload '] =requesthandlers.upload;handle['/show ']=requesthandlers.show;debugger;server.start (8080,router.route,handle);

Adding debug options When starting a service

Node Debug index.js

At this time to enter some instructions can be single-step debugging, to the breakpoint monitoring local variables, such as a command diagram, a lot of commands have their abbreviated form

node. js Debug Command

Command	Function
Run	Execute script, pause on first line
Restart	Re-execute the script
Cont, C	Continue execution until the next breakpoint is encountered
Next, N	Single Step execution
Step, S	Step into and enter the function
Out, O	Stepping out of a function
Setbreakpoint (), SB ()	The current line sets a breakpoint
Setbreakpoint (' F () '), SB (...)	Set a breakpoint on the first line of function f
Setbreakpoint (' Script.js '), SB (...)	Set breakpoints on line 20th of Script.js
Clearbreakpoint, CB (...)	Clear All Breakpoints
BackTrace, BT	Displays the current call stack
List (5)	Shows the front and back 5 lines of code that are currently executing
Watch (expr)	Adding expression expr to the watch list
Unwatch (expr)	Removing expression expr from the watch list
Watchers	Display all expressions and values in the watch list
Repl	Open an immediate evaluation environment in the current context
Kill	Terminates the currently executing script
Scripts	Show all scripts that are currently loaded
Version	Show V8 version

Detailed use of interested students can explore their own, I am not interested in ... It's too complicated to see a few intimate

Using Eclipse debugging

Yes, Eclipse is mighty, and even node. js can debug, download Eclipse on the Eclipe website, and Help->install New Software->add

Add a source in the popup window, the name is good to remember, the address is http://chromedevtools.googlecode.com/svn/update/dev/.

After a while, pop up the selection screen and select the first

All the way next to the final finish, the download will remind you to restart eclipse after completion, you can debug node. js, open the file you want to debug, switch Eclipse to debug view, click the small triangle on the right side of the toolbar, select Debug Configuration

Double-click the standard V8 VM option to create a new configuration and fill in the appropriate parameters.

To start the node server in the console via the--DEBUG-BRK option

Node--debug-brk=5858 test.js

Click the Debug button on the Eclipse interface just to debug node. js as you would debug Java

Debugging with Node-inspector

Most of the node. JS applications are Web applications, so some chrome-based online debugging tools came into being, the most famous should be Node-inspector, this is a node. js module, installation, use is quite convenient, First use NPM to install it in the global environment

NPM install-g Node-inspector

The node-inspector is switched to the debug input and output by WebSocket mode. Therefore, we need to start node-inspector to listen to the debug debug port of node. js before debugging. By default, the port of Node-inspector is 8080 and can be set by parameter--web-port=[port].

After starting Node-inpspector, we can start the node. JS program by--debug or--DEBUG-BRK.

At this time you can access http://127.0.0.1:8888/debug?port=5858 using browser debugging, look at the interface, no need to say anything more

At last

Reference: node. JS Development Guide

PS: Personally think the last one is the most convenient

node. JS Debugging