issue_comments: 752882797

If you're using arrow functions, you can presumably use default parameters, not much difference in support. That would save you 9 bytes. But OTOH you need "use strict"; to use arrow functions etc, and that's 13 bytes.

Your latest 250-byte one, with use strict, gzips to 199 bytes. The following might be 292 bytes, but compresses to 204, basically the same, and works in any browser (well, IE9+) at all:

var datasette=datasette||{};datasette.plugins=function(){var d={};return{register:function(b,c,e){d[b]||(d[b]=[]);d[b].push([c,e])},call:function(b,c){c=c||{};var e=[];(d[b]||[]).forEach(function(a){a=a[0].apply(a[0],a[1].map(function(a){return c[a]}));void 0!==a&&e.push(a)});return e}}}();

Source for that is below; I replaced the [fn,parameters] because closure-compiler includes a polyfill for that, and I ran closure-compiler --language_out ECMASCRIPT3:

js 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((data) => { /* Call with the correct arguments */ var result = data[0].apply(data[0], data[1].map(parameter => args[parameter])); if (result !== undefined) { results.push(result); } }); return results; } }; })();