JSDev

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>.

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JSDev, 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:

/*<tag> <stuff>*/

/*<tag>(<condition>) <stuff>*/

There can be no space between the / and the . There can be no space between the 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 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>         */

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 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();
    }
}
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