There are some gotchas to building Spidermonkey with NSPR. First of all, you need to successfully build NSPR. The source code tarball for NSPR comes with the standard GNU autoconfigure tools. If you are on a 64-bit system, you need to execute configure with the -enable-64bit option; otherwise the build will quickly fail. You should then test the build by going to the test subdirectory, building the testsuite and executing it. You also need to modify SpiderMonkey’s Makefile.ref (I am assuming you are building SpiderMonkey 1.7 and not an earlier release) to include libnspr and the NSPR headers. Two compile time defines are needed. You can either define JS_HAS_FILE_OBJECT and JS_THREADSAFE in Makefile.ref or as command line arguments to make. After than you, should be able to successfully build SpiderMonkey with native File object support.
Now that we have js build with support for objects, what can we do with it. Well, I guess we should start with the expected Hello World script.
js> File.output.writeln("Hello World"); Hello World true js> File.output.writeln("Hello, world"); "OK" Hello, world OK js> File.output.writeln("Hello, world"); "" Hello, world js>
Notice that true is outputted unless you append something else as shown above. Here is another short example which demonstrates how to list the properties of the instance File object for the current directory.
js> dir = new File('.'); /home/fpm/js/. js> for ( i in dir ) print(i); length parent path name isDirectory isFile exists canRead canWrite canAppend canReplace isOpen type mode creationTime lastModified size hasRandomAccess hasAutoFlush position isNative js>print(dir.path); /home/fpm/js/. js>print(dir.size) 4096 js>
The next example shows how to list some information about files in the current directory.
js> dir = new File('.'); /home/fpm/js/. js> files = dir.list(); 'OK' OK js> for (i in files ) print (files[i].name + ' ' + files[i].size + ' ' + files[i].creationTime); music.xml 1081 Tue Jan 06 2009 17:37:14 GMT-0500 (EST) xml.js 259 Tue Dec 30 2008 18:23:22 GMT-0500 (EST) xml1.js 699 Tue Jan 06 2009 23:33:26 GMT-0500 (EST) 2.xml 96 Tue Jan 06 2009 22:41:37 GMT-0500 (EST) 3.xml 127 Wed Jan 07 2009 00:02:18 GMT-0500 (EST) multiply.js 249 Tue Dec 30 2008 17:49:02 GMT-0500 (EST) helloworld.js 88 Tue Dec 30 2008 17:12:50 GMT-0500 (EST) hw.js 124 Thu Jan 01 2009 00:24:38 GMT-0500 (EST) xml2.js 502 Wed Jan 07 2009 00:02:17 GMT-0500 (EST) regex.js 143 Tue Dec 30 2008 18:10:55 GMT-0500 (EST) 1.xml 15 Tue Jan 06 2009 20:35:27 GMT-0500 (EST) js>
In the above example, list is an instance method of the File object. Using other File object instance methods, you can read data from a file and write data to a file.
In the following example, the script reads lines in from file.in and write the lines out to another file file.out, prepending each line with the corresponding line number.
#!/bin/js var filein = new File("file.in"); filein.open("read", "text"); var fileout = new File('file.out'); fileout.open("write,create", "text"); var n=1; while (data = filein.readln()) fileout.writeln(n++ + ' ' + data); filein.close(); fileout.close();
The File object provides two ways to access data inside a file: a text oriented access, based on characters, and a binary oriented access, based on bytes. In text mode, the maximum line length is 256 and the following encodings are supported: ASCII (text), UTF-8 and UCS-2. The File object has a number of instance methods including read, readLn, readAll, write, writeLn and writeAll. If you just want to copy the file in it’s entirety, you can use the copyTo method.
var file = new File("file.in"); file.open("read", "text"); file.copyTo("file.out"); file.close();
Similar instance methods which work on files include remove to delete a file or a directory and removeTo to rename a file.
Flaming disclaimer: Do not play with the File object if you are not prepared to have your hard drive erased, smashed, and broken into little bits! It mostly works right now, but no guarantees.
So far I have had no problem using the File object on my Fedora 10 64-bit platform but one never knows! Proceed with caution.