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JSDev, A JavaScript Development Tool
Douglas Crockford
douglas@crockford.com
2015-11-05
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:
/*<tag> <stuff>*/
/*<tag>(<condition>) <stuff>*/
There can be no space between the /* and the <tag>. There can be no space
between the <tag> and the (. The content of tagged comment may not include
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 of the names of the tags that should be activated.
Methods can be defined by following the tag name with : and a method name.
There can be no spaces around the :.
Replacement /*<tag> */
tag form { }
method form {<method>( );}
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." <input >output node test_expose enter:trace.enter exit:trace.exit unless:alert
JavaScript:
output = jsdev(input, [
"node",
"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"*/
}
/*node module.exports = 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");}
}
module.exports = Constructor;
lightly minified:
function Constructor(number) {
function private_method() {
}
this.priv = function () {
private_method();
}
}