issue_comments

Jest works with Puppeteer: https://jestjs.io/docs/en/puppeteer

I don't know if Jest on the command-line is the right tool for this. It works for the plugins.js script but I'm increasingly going to want to start adding tests for browser JavaScript features - like the https://github.com/simonw/datasette/blob/0.53/datasette/static/table.js script - which will need to run in a browser.

So maybe I should just find a browser testing solution and figure out how to run that under CI in GitHub Actions. Maybe https://www.cypress.io/ ?

Turned that into a TIL: https://til.simonwillison.net/javascript/jest-without-package-json

https://www.valentinog.com/blog/jest/ was useful.

I created a static/__tests__ folder and added this file as plugins.spec.js:

```javascript const datasette = require("../plugins.js");

describe("Datasette Plugins", () => { test("it should have datasette.plugins", () => { expect(!!datasette.plugins).toEqual(true); }); test("registering a plugin should work", () => { datasette.plugins.register("numbers", (a, b) => a + b, ["a", "b"]); var result = datasette.plugins.call("numbers", { a: 1, b: 2 }); expect(result).toEqual([3]); datasette.plugins.register("numbers", (a, b) => a * b, ["a", "b"]); var result2 = datasette.plugins.call("numbers", { a: 1, b: 2 }); expect(result2).toEqual([3, 2]); }); }); ```

In static/plugins.js I put this: ```javascript var datasette = datasette || {}; datasette.plugins = (() => { var registry = {}; return { register: (hook, fn, parameters) => { if (!registry[hook]) { registry[hook] = []; } registry[hook].push([fn, parameters]); }, call: (hook, args) => { args = args || {}; var results = []; (registry[hook] || []).forEach(([fn, parameters]) => { / Call with the correct arguments / var result = fn.apply(fn, parameters.map(parameter => args[parameter])); if (result !== undefined) { results.push(result); } }); return results; } }; })();

module.exports = datasette; `` Note themodule.exports` line at the end.

Then inside static/ I ran the following command:

``` % npx jest -c '{}' PASS tests/plugins.spec.js Datasette Plugins ✓ it should have datasette.plugins (3 ms) ✓ registering a plugin should work (1 ms)

Test Suites: 1 passed, 1 total Tests: 2 passed, 2 total Snapshots: 0 total Time: 1.163 s Ran all test suites. `` The-c {}was necessary because I didn't have a Jest configuration or apackage.json`.

https://twitter.com/dracos/status/1344402639476424706 points out that plugins returning 0 will be ignored.

This should probably check for result !== undefined instead - knocks the size up to 250.

This one minifies to 241: javascript var datasette = datasette || {}; datasette.plugins = (() => { var registry = {}; return { register: (hook, fn, parameters) => { if (!registry[hook]) { registry[hook] = []; } registry[hook].push([fn, parameters]); }, call: (hook, args) => { args = args || {}; var results = []; (registry[hook] || []).forEach(([fn, parameters]) => { /* Call with the correct arguments */ var result = fn.apply(fn, parameters.map(parameter => args[parameter])); if (result) { results.push(result); } }); return results; } }; })(); var datasette=datasette||{};datasette.plugins=(()=>{var a={};return{register:(t,r,e)=>{a[t]||(a[t]=[]),a[t].push([r,e])},call:(t,r)=>{r=r||{};var e=[];return(a[t]||[]).forEach(([a,t])=>{var s=a.apply(a,t.map(a=>r[a]));s&&e.push(s)}),e}}})();

FixMyStreet inlines some JavaScript, and it's always a good idea to copy what they're doing when it comes to web performance: https://github.com/mysociety/fixmystreet/blob/23e9564b58a86b783ce47f3c0bf837cbd4fe7282/templates/web/base/common_header_tags.html#L19-L25

Note var fixmystreet=fixmystreet||{}; which is shorter - https://twitter.com/dracos/status/1344399909794045954

If I implement this I can automate the CodeMirror minification and remove the bit about running uglify-js against it from the documentation here: https://docs.datasette.io/en/0.53/contributing.html#upgrading-codemirror

If I'm going to minify table.js I'd like to offer a source map for it.

Running https://skalman.github.io/UglifyJS-online/ against https://github.com/simonw/datasette/blob/0.53/datasette/static/table.js knocks it down from 7810 characters to 4643.

Another option: have both "dev" and "production" versions of the plugin mechanism script. Make it easy to switch between the two. Build JavaScript unit tests that exercise the "production" APIs against the development version, and have extra tests that just work against the features in the development version.

Started a Twitter thread about this here: https://twitter.com/simonw/status/1344392603794477056

This one is 683 bytes with Uglify - I like how https://skalman.github.io/UglifyJS-online/ shows you the minified character count as you edit the script: ```javascript window.datasette = window.datasette || {}; window.datasette.plugins = (() => { var registry = {}; var definitions = {}; var stringify = JSON.stringify;

function extractParameters(fn) {
    var match = /\((.*)\)/.exec(fn.toString());
    if (match && match[1].trim()) {
        return match[1].split(',').map(s => s.trim());
    } else {
        return [];
    }
}

function isSubSet(a, b) {
    return a.every(parameter => b.includes(parameter))
}

return {
    _r: registry,
    define: (hook, parameters) => {
        definitions[hook] = parameters || [];
    },
    register: (hook, fn, parameters) => {
        parameters = parameters || extractParameters(fn);
        if (!definitions[hook]) {
            throw 'Hook "' + hook + '" not defined';
        }
        /* Check parameters is a subset of definitions[hook] */
        var validParameters = definitions[hook];
        if (!isSubSet(parameters, validParameters)) {
            throw '"' + hook + '" valid args: ' + stringify(validParameters);
        }
        if (!registry[hook]) {
            registry[hook] = [];
        }
        registry[hook].push([fn, parameters]);
    },

    call: (hook, args) => {
        args = args || {};
        if (!definitions[hook]) {
            throw '"' + hook + '" hook not defined';
        }
        if (!isSubSet(Object.keys(args), definitions[hook])) {
            throw '"' + hook + '" valid args: ' + stringify(definitions[hook]);
        }

        var implementations = registry[hook] || [];
        var results = [];
        implementations.forEach(([fn, parameters]) => {
            /* Call with the correct arguments */
            var callWith = parameters.map(parameter => args[parameter]);
            var result = fn.apply(fn, callWith);
            if (result) {
                results.push(result);
            }
        });
        return results;
    }       
};

})(); ``window.datasette=window.datasette||{},window.datasette.plugins=(()=>{var t={},r={},e=JSON.stringify;function i(t,r){return t.every(t=>r.includes(t))}return{_r:t,define:(t,e)=>{r[t]=e||[]},register:(a,n,o)=>{if(o=o||function(t){var r=/((.*))/.exec(t.toString());return r&&r[1].trim()?r[1].split(",").map(t=>t.trim()):[]}(n),!r[a])throw'Hook "'+a+'" not defined';var d=r[a];if(!i(o,d))throw'"'+a+'" valid args: '+e(d);t[a]||(t[a]=[]),t[a].push([n,o])},call:(a,n)=>{if(n=n||{},!r[a])throw'"'+a+'" hook not defined';if(!i(Object.keys(n),r[a]))throw'"'+a+'" valid args: '+e(r[a]);var o=t[a]||[],d=[];return o.forEach(([t,r])=>{var e=r.map(t=>n[t]),i=t.apply(t,e);i&&d.push(i)}),d}}})();`

I'm going to write a few example plugins and try them out against the longer and shorter versions of the script, to get a better feel for how useful the longer versions with the error handling and explicit definition actually are.

I gotta admit that 262 byte version is pretty tempting, if it's going to end up in the <head> of every single page.

262 bytes if I remove the parameter introspection code, instead requiring plugin authors to specify the arguments they take: javascript window.datasette = window.datasette || {}; window.datasette.plugins = (() => { var registry = {}; return { register: (hook, fn, parameters) => { if (!registry[hook]) { registry[hook] = []; } registry[hook].push([fn, parameters]); }, call: (hook, args) => { args = args || {}; var results = []; (registry[hook] || []).forEach(([fn, parameters]) => { /* Call with the correct arguments */ var callWith = parameters.map(parameter => args[parameter]); var result = fn.apply(fn, callWith); if (result) { results.push(result); } }); return results; } }; })(); window.datasette=window.datasette||{},window.datasette.plugins=(()=>{var a={};return{register:(t,e,r)=>{a[t]||(a[t]=[]),a[t].push([e,r])},call:(t,e)=>{e=e||{};var r=[];return(a[t]||[]).forEach(([a,t])=>{var s=t.map(a=>e[a]),d=a.apply(a,s);d&&r.push(d)}),r}}})();

Removing the datasette.plugin.define() method and associated error handling reduces the uglified version from 683 bytes to 380 bytes. I think the error checking is worth the extra 303 bytes per page load, even if it's only really needed for a better developer experience. ```javascript window.datasette = window.datasette || {}; window.datasette.plugins = (() => { var registry = {};

function extractParameters(fn) {
    var match = /\((.*)\)/.exec(fn.toString());
    if (match && match[1].trim()) {
        return match[1].split(',').map(s => s.trim());
    } else {
        return [];
    }
}
return {
    register: (hook, fn, parameters) => {
        parameters = parameters || extractParameters(fn);
        if (!registry[hook]) {
            registry[hook] = [];
        }
        registry[hook].push([fn, parameters]);
    },

    call: (hook, args) => {
        args = args || {};
        var implementations = registry[hook] || [];
        var results = [];
        implementations.forEach(([fn, parameters]) => {
            /* Call with the correct arguments */
            var callWith = parameters.map(parameter => args[parameter]);
            var result = fn.apply(fn, callWith);
            if (result) {
                results.push(result);
            }
        });
        return results;
    }
};

})(); ``window.datasette=window.datasette||{},window.datasette.plugins=(()=>{var t={};return{register:(r,a,e)=>{e=e||function(t){var r=/((.*))/.exec(t.toString());return r&&r[1].trim()?r[1].split(",").map(t=>t.trim()):[]}(a),t[r]||(t[r]=[]),t[r].push([a,e])},call:(r,a)=>{a=a||{};var e=t[r]||[],i=[];return e.forEach(([t,r])=>{var e=r.map(t=>a[t]),n=t.apply(t,e);n&&i.push(n)}),i}}})();`

https://jestjs.io/ looks worth trying here.

I'm going to need to add JavaScript unit tests for this new plugin system.

I don't want Datasette contributors to need a working Node.js install to run the tests or work on Datasette unless they are explicitly working on the JavaScript.

I think I'm going to do this with a unit test that runs only if upglify-js is available on the path and confirms that the *.min.js version of each script in the repository correctly matches the results from running uglify-js against it.

That way if anyone checks in a change to JavaScript but forgets to run the minifier the tests will fail in CI.

I tried a few different pure-Python JavaScript minifying libraries and none of them produced results as good as https://www.npmjs.com/package/uglify-js for the plugin code I'm considering in #983.

So I think I'll need to rely on a Node.js tool for this.

This version minifies to 702 characters: ```javascript window.datasette = window.datasette || {}; window.datasette.plugins = (() => { var registry = {}; var definitions = {}; var stringify = JSON.stringify;

function extractParameters(fn) {
    var match = /\((.*)\)/.exec(fn.toString());
    if (match && match[1].trim()) {
        return match[1].split(',').map(s => s.trim());
    } else {
        return [];
    }
}

function isSubSet(a, b) {
    return a.every(parameter => b.includes(parameter))
}

return {
    _registry: registry,
    define: (hook, parameters) => {
        definitions[hook] = parameters || [];
    },
    register: (hook, fn, parameters) => {
        parameters = parameters || extractParameters(fn);
        if (!definitions[hook]) {
            throw '"' + hook + '" is not a defined hook';
        }
        /* Check parameters is a subset of definitions[hook] */
        var validParameters = definitions[hook];
        if (!isSubSet(parameters, validParameters)) {
            throw '"' + hook + '" valid args are ' + stringify(validParameters);
        }
        if (!registry[hook]) {
            registry[hook] = [];
        }
        registry[hook].push([fn, parameters]);
    },

    call: (hook, args) => {
        args = args || {};
        if (!definitions[hook]) {
            throw '"' + hook + '" hook is not defined';
        }
        if (!isSubSet(Object.keys(args), definitions[hook])) {
            throw '"' + hook + '" valid args: ' + stringify(definitions[hook]);
        }

        var implementations = registry[hook] || [];
        var results = [];
        implementations.forEach(([fn, parameters]) => {
            /* Call with the correct arguments */
            var callWith = parameters.map(parameter => args[parameter]);
            var result = fn.apply(fn, callWith);
            if (result) {
                results.push(result);
            }
        });
        return results;
    }       
};

})(); ``` Or 701 characters using https://skalman.github.io/UglifyJS-online/

Using raw string exceptions, throw '"' + hook + '" hook has not been defined';, knocks it down to 795 characters.

If I'm going to minify it I'll need to figure out a build step in Datasette itself so that I can easily work on that minified version.

I need to decide how this code is going to be loaded. Putting it in a blocking <script> element in the head would work, but I'd rather not block loading of the rest of the page. Using a <script async> method would be nicer, but then I have to worry about plugins attempting to register themselves before the page has fully loaded.

Running it through https://javascript-minifier.com/ produces this, which is 855 characters - so maybe I could inline that into the header of the page?

window.datasette={},window.datasette.plugins=function(){var r={},n={};function e(r,n){return r.every(r=>n.includes(r))}return{define:function(r,e){n[r]=e||[]},register:function(t,i,o){if(o=o||function(r){var n=/\((.*)\)/.exec(r.toString());return n&&n[1].trim()?n[1].split(",").map(r=>r.trim()):[]}(i),!n[t])throw new Error('"'+t+'" is not a defined plugin hook');if(!n[t])throw new Error('"'+t+'" is not a defined plugin hook');var a=n[t];if(!e(o,a))throw new Error('"'+t+'" valid parameters are '+JSON.stringify(a));r[t]||(r[t]=[]),r[t].push([i,o])},_registry:r,call:function(t,i){if(i=i||{},!n[t])throw new Error('"'+t+'" hook has not been defined');if(!e(Object.keys(i),n[t]))throw new Error('"'+t+'" valid arguments are '+JSON.stringify(n[t]));var o=r[t]||[],a=[];return o.forEach(([r,n])=>{var e=n.map(r=>i[r]),t=r.apply(r,e);t&&a.push(t)}),a}}}();

This version adds datasette.plugins.define() plus extra validation of both .register() and .call(): ```javascript window.datasette = {}; window.datasette.plugins = (function() { var registry = {}; var definitions = {};

function extractParameters(fn) {
    var match = /\((.*)\)/.exec(fn.toString());
    if (match && match[1].trim()) {
        return match[1].split(',').map(s => s.trim());
    } else {
        return [];
    }
}

function define(hook, parameters) {
    definitions[hook] = parameters || [];
}

function isSubSet(a, b) {
    return a.every(parameter => b.includes(parameter))
}

function register(hook, fn, parameters) {
    parameters = parameters || extractParameters(fn);
    if (!definitions[hook]) {
        throw new Error('"' + hook + '" is not a defined plugin hook');
    }
    if (!definitions[hook]) {
        throw new Error('"' + hook + '" is not a defined plugin hook');
    }
    /* Check parameters is a subset of definitions[hook] */
    var validParameters = definitions[hook];
    if (!isSubSet(parameters, validParameters)) {
        throw new Error('"' + hook + '" valid parameters are ' + JSON.stringify(validParameters));
    }
    if (!registry[hook]) {
        registry[hook] = [];
    }
    registry[hook].push([fn, parameters]);
}

function call(hook, args) {
    args = args || {};
    if (!definitions[hook]) {
        throw new Error('"' + hook + '" hook has not been defined');
    }
    if (!isSubSet(Object.keys(args), definitions[hook])) {
        throw new Error('"' + hook + '" valid arguments are ' + JSON.stringify(definitions[hook]));
    }

    var implementations = registry[hook] || [];
    var results = [];
    implementations.forEach(([fn, parameters]) => {
        /* Call with the correct arguments */
        var callWith = parameters.map(parameter => args[parameter]);
        var result = fn.apply(fn, callWith);
        if (result) {
            results.push(result);
        }
    });
    return results;
}
return {
    define: define,
    register: register,
    _registry: registry,
    call: call
};

})(); Usage:javascript datasette.plugins.define('numbers', ['a', 'b']) datasette.plugins.register('numbers', (a, b) => a + b) datasette.plugins.register('numbers', (a, b) => a * b) datasette.plugins.call('numbers', {a: 4, b: 6}) ```

This could work to define a plugin hook: javascript datasette.plugins.define('numbers', ['a' ,'b'])

This implementation doesn't have an equivalent of "hookspecs" which can identify if a registered plugin implementation matches a known signature. I should add that, it will provide a better developer experience if someone has a typo.

Initial prototype: ```javascript window.datasette = {}; window.datasette.plugins = (function() { var registry = {};

function extractParameters(fn) {
    var match = /\((.*)\)/.exec(fn.toString());
    if (match && match[1].trim()) {
        return match[1].split(',').map(s => s.trim());
    } else {
        return [];
    }
}

function register(hook, fn, parameters) {
    parameters = parameters || extractParameters(fn);
    if (!registry[hook]) {
        registry[hook] = [];
    }
    registry[hook].push([fn, parameters]);
}

function call(hook, args) {
    args = args || {};
    var implementations = registry[hook] || [];
    var results = [];
    implementations.forEach(([fn, parameters]) => {
        /* Call with the correct arguments */
        var callWith = parameters.map(parameter => args[parameter]);
        var result = fn.apply(fn, callWith);
        if (result) {
            results.push(result);
        }
    });
    return results;
}
return {
    register: register,
    _registry: registry,
    call: call
};

})(); Usage example:javascript datasette.plugins.register('numbers', (a, b) => a + b) datasette.plugins.register('numbers', (a, b) => a * b) datasette.plugins.call('numbers', {a: 4, b: 6}) / Returns [10, 24] / ```

The column_actions hook is the obvious first place to try this out. What are some demo plugins I could build for it?

• Word cloud for this column
• Count values (essentially linking to the SQL query for that column, as an extended version of the facet counts) - would be great if this could include pagination somehow, via #856.
• Extract this column into a separate table
• Add an index to this column

Then to call the plugins: javascript datasette.plugins.call('column_actions', {database: 'database', table: 'table'})

Potential design: javascript datasette.plugins.register('column_actions', function(database, table, column, actor) { /* ... *l }) Or if you want to be explicit to survive minification: javascript datasette.plugins.register('column_actions', function(database, table, column, actor) { /* ... *l }, ['database', 'table', 'column', 'actor']) I'm making that list of parameter names an optional third argument to the register() function. If that argument isn't passed, introspection will be used to figure out the parameter names.

Pluggy does dependency injection by introspecting the named arguments to the Python function, which I really like.

That's tricker in JavaScript. It looks like the only way to introspect a function is to look at the .toString() representation of it and parse the (parameter, list) using a regular expression.

Even more challenging: JavaScript developers love minifying their code, and minification can shorten the function parameter names.

From https://code-maven.com/dependency-injection-in-angularjs it looks like Angular.js does dependency injection and solves this by letting you optionally provide a separate list of the arguments your function uses:

javascript angular.module('DemoApp', []) .controller('DemoController', ['$scope', '$log', function($scope, $log) { $scope.message = "Hello World"; $log.debug('logging hello'); }]);

I can copy that approach: I'll introspect by default, but provide a documented mechanism for explicitly listing your parameter names so that if you know your plugin code will be minified you can use that instead.

I'm going to introduce a global datasette object which holds all the documented JavaScript API for plugin authors.

I think I'm going to try building a very lightweight clone of the core API design of Pluggy - not the advanced features, just the idea that plugins can register and a call to plugin.nameOfHook() will return the concatenated results of all of the registered hooks.

In terms of "places to put your plugin content", the simplest solution I can think of is something like this: ```html

``` Alternative designs:

• A documented JavaScript function that returns the CSS selector where plugins should put their content
• A documented JavaScript function that returns a DOM node where plugins should put their content. This would allow the JavaScript to create the element if it does not already exist (though it wouldn't be obvious WHERE that element should be created)
• Documented JavaScript functions for things like "append this node/HTML to the place-where-plugins-go"

I think the original option - an empty <div> with a known id attribute - is the right one to go with here. It's the simplest, it's very easy for custom template authors to understand and it acknowledges that plugins may have all kinds of extra crazy stuff they want to do - like checking in that div to see if another plugin has written to it already, for example.

Related problem: right now if you're writing custom template it's not at all obvious how to write them such that visualization plugins like datasette-cluster-map will continue to work.

More generally, I need to document certain areas of the page that JavaScript plugins are invited to append their content to - such that plugin authors can use them and feel confident that future changes to the Datasette templates won't break their plugins.