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When developer calls setBreakpoint with an unknown script name,
we convert the script name into regular expression matching all
paths ending with given name (name can be a relative path too).
To create such breakpoint in V8, we use type `scriptRegEx`
instead of `scriptId` for `setbreakpoint` request.
To restore such breakpoint, we save the original script name
send by the user. We use this original name to set (restore)
breakpoint in the new child process.
This is a back-port of commit 5db936d from the master branch.
170 lines
4.9 KiB
Markdown
170 lines
4.9 KiB
Markdown
# Debugger
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Stability: 3 - Stable
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<!-- type=misc -->
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V8 comes with an extensive debugger which is accessible out-of-process via a
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simple [TCP protocol](http://code.google.com/p/v8/wiki/DebuggerProtocol).
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Node has a built-in client for this debugger. To use this, start Node with the
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`debug` argument; a prompt will appear:
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% node debug myscript.js
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< debugger listening on port 5858
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connecting... ok
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break in /home/indutny/Code/git/indutny/myscript.js:1
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1 x = 5;
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2 setTimeout(function () {
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3 debugger;
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debug>
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Node's debugger client doesn't support the full range of commands, but
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simple step and inspection is possible. By putting the statement `debugger;`
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into the source code of your script, you will enable a breakpoint.
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For example, suppose `myscript.js` looked like this:
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// myscript.js
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x = 5;
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setTimeout(function () {
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debugger;
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console.log("world");
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}, 1000);
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console.log("hello");
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Then once the debugger is run, it will break on line 4.
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% node debug myscript.js
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< debugger listening on port 5858
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connecting... ok
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break in /home/indutny/Code/git/indutny/myscript.js:1
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1 x = 5;
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2 setTimeout(function () {
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3 debugger;
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debug> cont
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< hello
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break in /home/indutny/Code/git/indutny/myscript.js:3
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1 x = 5;
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2 setTimeout(function () {
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3 debugger;
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4 console.log("world");
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5 }, 1000);
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debug> next
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break in /home/indutny/Code/git/indutny/myscript.js:4
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2 setTimeout(function () {
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3 debugger;
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4 console.log("world");
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5 }, 1000);
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6 console.log("hello");
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debug> repl
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Press Ctrl + C to leave debug repl
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> x
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5
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> 2+2
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4
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debug> next
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< world
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break in /home/indutny/Code/git/indutny/myscript.js:5
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3 debugger;
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4 console.log("world");
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5 }, 1000);
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6 console.log("hello");
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7
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debug> quit
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%
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The `repl` command allows you to evaluate code remotely. The `next` command
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steps over to the next line. There are a few other commands available and more
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to come. Type `help` to see others.
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## Watchers
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You can watch expression and variable values while debugging your code.
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On every breakpoint each expression from the watchers list will be evaluated
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in the current context and displayed just before the breakpoint's source code
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listing.
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To start watching an expression, type `watch("my_expression")`. `watchers`
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prints the active watchers. To remove a watcher, type
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`unwatch("my_expression")`.
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## Commands reference
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### Stepping
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* `cont`, `c` - Continue execution
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* `next`, `n` - Step next
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* `step`, `s` - Step in
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* `out`, `o` - Step out
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* `pause` - Pause running code (like pause button in Developer Tools)
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### Breakpoints
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* `setBreakpoint()`, `sb()` - Set breakpoint on current line
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* `setBreakpoint(line)`, `sb(line)` - Set breakpoint on specific line
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* `setBreakpoint('fn()')`, `sb(...)` - Set breakpoint on a first statement in
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functions body
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* `setBreakpoint('script.js', 1)`, `sb(...)` - Set breakpoint on first line of
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script.js
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* `clearBreakpoint`, `cb(...)` - Clear breakpoint
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It is also possible to set a breakpoint in a file (module) that
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isn't loaded yet:
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% ./node debug test/fixtures/break-in-module/main.js
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< debugger listening on port 5858
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connecting to port 5858... ok
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break in test/fixtures/break-in-module/main.js:1
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1 var mod = require('./mod.js');
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2 mod.hello();
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3 mod.hello();
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debug> setBreakpoint('mod.js', 23)
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Warning: script 'mod.js' was not loaded yet.
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1 var mod = require('./mod.js');
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2 mod.hello();
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3 mod.hello();
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debug> c
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break in test/fixtures/break-in-module/mod.js:23
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21
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22 exports.hello = function() {
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23 return 'hello from module';
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24 };
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25
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debug>
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### Info
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* `backtrace`, `bt` - Print backtrace of current execution frame
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* `list(5)` - List scripts source code with 5 line context (5 lines before and
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after)
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* `watch(expr)` - Add expression to watch list
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* `unwatch(expr)` - Remove expression from watch list
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* `watchers` - List all watchers and their values (automatically listed on each
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breakpoint)
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* `repl` - Open debugger's repl for evaluation in debugging script's context
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### Execution control
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* `run` - Run script (automatically runs on debugger's start)
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* `restart` - Restart script
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* `kill` - Kill script
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### Various
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* `scripts` - List all loaded scripts
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* `version` - Display v8's version
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## Advanced Usage
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The V8 debugger can be enabled and accessed either by starting Node with
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the `--debug` command-line flag or by signaling an existing Node process
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with `SIGUSR1`.
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Once a process has been set in debug mode with this it can be connected to
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with the node debugger. Either connect to the `pid` or the URI to the debugger.
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The syntax is:
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* `node debug -p <pid>` - Connects to the process via the `pid`
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* `node debug <URI> - Connects to the process via the URI such as localhost:5858
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