JSDev, A JavaScript Development Tool

Douglas Crockford [email protected]

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();
    }
}