Node.js Manual & Documentation

Table Of Contents

Debugger 调试器

V8 comes with an extensive debugger which is accessible out-of-process via a simple TCP protocol. Node has a built-in client for this debugger. To use this, start Node with the debug argument; a prompt will appear:

V8引擎自身配备了全面的调试器，该调试器通过简单的TCP协议在进程外访问。Node中内置了该调试器的客户端，要使用它可以在启动Node时附加debug参数，此模式下将显示debug提示符：

% node debug myscript.js
debug>

At this point myscript.js is not yet running. To start the script, enter the command run. If everything works okay, the output should look like this:

此时 myscript.js还没有开始执行，若要执行这段脚本，还需要输入run命令。如果一切运行正常的话输出信息应该如下所示：

% node debug myscript.js
debug> run
debugger listening on port 5858
connecting...ok

Node's debugger client doesn't support the full range of commands, but simple step and inspection is possible. By putting the statement debugger; into the source code of your script, you will enable a breakpoint.

Node的调试器客户端虽然没有支持所有的命令，但是实现简单的单步调试还是可以的。你可以在脚本代码中声明debugger;语句从而启用一个断点。

For example, suppose myscript.js looked like this:

例如，假设myscript.js代码如下：

// myscript.js
x = 5;
setTimeout(function () {
  debugger;
  console.log("world");
}, 1000);
console.log("hello");

Then once the debugger is run, it will break on line 4.

一旦调试器开始运行，那么它将在执行到第4行代码处时停止。

% ./node debug myscript.js
debug> run
debugger listening on port 5858
connecting...ok
hello
break in #<an Object>._onTimeout(), myscript.js:4
  debugger;
  ^
debug> next
break in #<an Object>._onTimeout(), myscript.js:5
  console.log("world");
  ^
debug> print x
5
debug> print 2+2
4
debug> next
world
break in #<an Object>._onTimeout() returning undefined, myscript.js:6
}, 1000);
^
debug> quit
A debugging session is active. Quit anyway? (y or n) y
%

The print command allows you to evaluate variables. The next command steps over to the next line. There are a few other commands available and more to come type help to see others.

print命令允许将变量输出到控制台进行查看。next命令单步调试到下一行代码。还有其他一些可用的命令你可以通过输入help进行查看。

Advanced Usage 高级用法

The V8 debugger can be enabled and accessed either by starting Node with the --debug command-line flag or by signaling an existing Node process with SIGUSR1.

要启用V8引擎调试器你可以在启动Node时增加命令行参数--debug或者给一个已经存在的Node进程发送值为SIGUSR1的信号量。