JSDev is a simple JavaScript preprocessor. It implements a tiny macro language that is written in the form of tagged comments. These comments are normally ignored, and will be removed by JSMin. But JSDev will activate these comments, replacing them with executable forms that can be used to do debugging, testing, logging, or tracing. JSDev scans a source looking for and replacing patterns. A pattern is a slashstar comment containing a tag and some stuff, and optionally a condition wrapped in parens. There must be no space between the slashstar and the <tag>.
npm install JSDevJSDev, A JavaScript Development Tool
Douglas Crockford
douglas@crockford.com
2012-01-05
JSDev is a filter that activates selected comments, making them executable.
This makes it possible to put development, performance, and testing scaffolding
into a source file. The scaffolding is removed by minification, but is activated
by JSDev.
JSDev is a filter that takes a source file and looks for tagged comments in
either of these forms:
/
/
There can be no space between the /* and the
between the
comments, nor can it contain strings or regular expression literals that
contain */. So, write
/debug(/[a-z][a-z0-9]/.test(variable))
console.log("*/ test");
*/
as
/debug(/[a-z][a-z0-9](?:)/.test(variable))
console.log("*\/ test");
*/
JSDev is given a list the names of the tags that should be activated.
Also, methods can be defined by following the tag name with : and a method
name. There can be no spaces around the :.
Replacement /
tag form { }
method form {
If a condition was included, then the replacement will be preceded with an
if statement.
The implementation in C obtains the input from stdin, and provides the result
to stdout. The tag list is taken from the command line. The command line can
also include a -comment specification. JSDev will exit(1) if there is an error.
In JavaScript, it is available as the JSDEV function that takes a source,
an array of tags, and an optional array of comments. It will throw an
exception if there is an error.
C command line example:
jsdev -comment "Devel Edition." output test_expose enter:trace.enter exit:trace.exit unless:alert
JavaScript:
output = JSDEV(input, [
"test_expose",
"enter:trace.enter",
"exit:trace.exit",
"unless:alert"
] , ["Devel Edition."]);
input:
// This is a sample file.
function Constructor(number) {
/enter 'Constructor'/
/unless(typeof number !== 'number') 'number', "Type error"/
function private_method() {
/enter 'private_method'/
/exit 'private_method'/
}
/*test_expose
this.private_method = private_method;
*/
this.priv = function () {
/enter 'priv'/
private_method();
/exit 'priv'/
}
/exit "Constructor"/
}
output:
// Devel Edition.
// This is a sample file.
function Constructor(number) {
{trace.enter('Constructor');}
if (typeof number !== 'number') {alert('number', "Type error");}
function private_method() {
{trace.enter('private_method');}
{trace.exit('private_method');}
}
{
this.private_method = private_method;
}
this.priv = function () {
{trace.enter('priv');}
private_method();
{trace.exit('priv');}
}
{trace.exit("Constructor");}
}
lightly minified:
function Constructor(number) {
function private_method() {
}
this.priv = function () {
private_method();
}
}