3f:null 40:["$","title",null,{"children":"interfaces for function types | Riley | Observable"}] 46:T5a5,

interfaces for function types

This is an extension of another notebook that adds the ability to detect types of functions. Using this, you can detect

async functions,
generator functions,
functions from different realms,
function expressions,
class expressions, and
arrow function expressions.

The like object exposed is the same object as the original, with the func property replaced with func.

47:T67c,

`func` type functions

This ${typer.class.name} has additional properties for handling various types of functions. func.local or func.local.not tests for a function that does or does not inherit from this realm’s Function class, respectively.
func.bindable tests for a function that can use bindings to this, arguments, and super. This is any function that is not an arrow function.
func.class === funcByClass
func.form === funcByForm48:T7f9,### by class This is a plain object that holds ${typer.class.name}s for distinguishing functions by class, specifically looking at the async and generator behaviors. These should work whether or not the provided function is in the same realm.

funcByClass.basic tests for any function that is neither an async function nor a generator function.
funcByClass.async tests for any async function.
funcByClass.async.only tests for any async function that is not a generator function.
funcByClass.generator tests for any generator function.
funcByClass.generator.only tests for any generator function that is not an async function.
funcByClass.asyncGenerator tests for any async function that is also a generator function.

49:Tba1,### by form This is a plain object that holds ${typer.class.name}s for distinguishing functions by syntactic form, such as function expressions, class expressions, and arrow function expressions. This is achieved by parsing functions’ entire source code using Acorn. Because the context of functions’ source codes cannot be accessed, it is impossible to distinguish between expressions and their equivalent declarations.

funcByForm.function tests for functions created from function declarations, function expressions, or new ${Function.name}(…).
funcByForm.class tests for functions directly created from class declarations or class expressions.
funcByForm.arrow tests for arrow functions.
funcByForm.native tests for functions written in the JavaScript engine’s native code. This is usually depicted as a function with an empty body except for [native code]. Be warned that bound functions tend to show up as native functions.
funcByForm.unknown tests for functions with syntax that could not be parsed and do not look like native functions.

4a:T5dc,# querying types directly If you would prefer to directly ask for a function’s properties rather than using ${typer.class.name}s, then just pass any function into ${funcClass.name} or ${funcForm.name}. Unless ${funcForm.name} throws an error, both functions will always output one of a set of values. Each function’s possible return values are the enumerable values of the enums property on the function. The return values are immutable and can be checked against with ===. Because the relevant characteristics of functions are largely immutable, a WeakMap is used to cache the results, when it’s supported. Don’t change the prototypes of functions, or ${funcClass.name} will provide wrong answers. Overriding a function’s ${Function.prototype.toString.name} method will not affect results.4b:T564,funcForm = { const cache = globalThis.WeakMap ? new globalThis.WeakMap() : null; const forms = makeNull(true, { "function": "function", "class": "class", arrow: "=>", native: "native", "unknown": null, [Symbol.toStringTag]: "function forms" }); Object.defineProperties(funcForm, { enums: { enumerable: true, value: forms } }); return funcForm; function funcForm(func) { if (typeof func !== "function") { throw new TypeError("not a function"); } if (cache?.has(func)) { return cache.get(func); } let n; try { n = Acorn.parse(funcToString(func), { allowReserved: true }); } catch (e) { if (e !== null && typeof e === "object" && e instanceof SyntaxError && e.loc && (typeof e.pos === "number")) { if (funcToString(func).match(/{\s*\[native code\]\s*}\s*$/)) { return forms.native; } } throw e; } n.type == "Program" && (n = n.body[0]); n.type == "ExpressionStatement" && (n = n.expression); switch (n.type) { case "FunctionDeclaration": return forms.function; case "ClassDeclaration": return forms.class; case "ArrowFunctionExpression": return forms.arrow; } return forms.unknown; } function funcToString(f) { return Function.prototype.toString.call(f); } }4c:Ta93,funcClass = { const cache = globalThis.WeakMap ? new globalThis.WeakMap() : null; const [fAsync, fGen, fAsyncGen] = [ async function() {}, function*() {}, async function*() {} ].map(f => Object.getPrototypeOf(f).constructor); const classes = makeNull(true, { basic: makeNull(true, { "async": false, "generator": false, [Symbol.toStringTag]: "basic" }), "async": makeNull(true, { "async": true, "generator": false, [Symbol.toStringTag]: "async only" }), gen: makeNull(true, { "async": false, "generator": true, [Symbol.toStringTag]: "generator only" }), asyncGen: makeNull(true, { "async": true, "generator": true, [Symbol.toStringTag]: "async & generator" }), [Symbol.toStringTag]: "function classes" }); Object.defineProperties(funcClass, { enums: { enumerable: true, value: classes }, classes: { enumerable: true, value: Object.create(null, { basic: {enumerable: true, value: Function}, "async": {enumerable: true, value: fAsync}, gen: {enumerable: true, value: fGen}, asyncGen: {enumerable: true, value: fAsyncGen}, [Symbol.toStringTag]: {value: "function classes"} }) } }); return funcClass; function funcClass(func) { if (typeof func !== "function") { throw new TypeError("not a function"); } if (cache?.has(func)) { return cache.get(func); } const external = !(func instanceof Function); if (!external) { // test for class if (func instanceof fAsyncGen) { return funcClass.enums.asyncGen; } else if (func instanceof fAsync) { return funcClass.enums.async; } else if (func instanceof fGen) { return funcClass.enums.gen; } else { return funcClass.enums.basic; } } else { // function from another realm // find class objects in other realm let protos = [func]; do { protos.unshift(Object.getPrototypeOf(protos[0])); } while (protos[0] !== null); protos.shift(); let externalFn = protos[1].constructor; // external `Function` class protos.length = 0; let [eAsync, eGen, eAsyncGen] = new externalFn(`return [ async function() {}, function*() {}, async function*() {} ].map(f => Object.getPrototypeOf(f).constructor);`)(); // test for class if (func instanceof eAsyncGen) { return classes.asyncGen; } else if (func instanceof eAsync) { return classes.async; } else if (func instanceof eGen) { return classes.gen; } else { return classes.basic; } } } }4d:T6a8,{ const headers = Object.freeze(["function", "class", "class ❌", "form", "form ❌"].filter(prop => testFuncs.some(row => prop in row))); return htl.html`${headers.map(th => th.includes("❌") ? htl.html`` : htl.html``)} ${testFuncs.map(row => htl.html`${ headers.map(prop => prop in row ? htl.html`` : htl.html``) }`)}

${th.replaceAll("❌", "").trim()}	${th}
${format(row[prop])}	${"\u2713"}

`; function format(v) { switch (v === null ? "null" : typeof v) { case "string": v = htl.html`

${JSON.stringify(v)}`;
        break;
      case "function":
        v = Function.prototype.toString.call(v);
        try {
          v = md`~~~js${"\n"}${v}${"\n"}~~~`;
        } catch {
          v = htl.html`${v}`;
        }
        break;
      case "object":
        switch (Object.getPrototypeOf(v)) {
          case null:
          case Object.prototype:
            v = md`~~~json${"\n"}${JSON.stringify(v, undefined, "\t")}${"\n"}~~~`;
            break;
          default:
            try {
              v = inspect(v);
              v.style.display = "inline-block";
              v.style.maxWidth = "24em";
            } catch {
              v = String(v);
            }
        }
        break;
      case "undefined":
      case "null":
        v = htl.html`${String(v)}`;
    }
    return v;
  }
}4e:T565,testFuncs = {
  function strTag() { return [this.fnClass, this.form].map(o => typeof o === "string" ? o : (o[Symbol.toStringTag] || String(o))).join(" ").trim(); }
  function eq(a, b) { return (a === b) || (JSON.stringify(a, undefined, "") === JSON.stringify(b, undefined, "")) }

  return [
    [function a() { return; }, "function", "basic"],
    [async function b(a, ...b) { return b; }, "function", "async"],
    [async function* c(a, ...b) { yield b; }, "function", "asyncGen"],
    [() => {}, "arrow", "basic"],
    [(a, b, c = async function* potate() {}) => {}, "arrow", "basic"],
    [class CLASS extends Array {}, "class", "basic"],
    [Array.prototype.at, "native", "basic"]

  ].map(([f, form, fnClass]) => {
    let o = Object.create(null);
    o.function = f;
    o.form = typeof form == "string" ? funcForm.enums[form] : form;
    if (!o.form) { throw new TypeError(`not a function form: ${o.form ?? form}`)}
    form = funcForm(f);
    console.dir(form);
    eq(o.form, form) || (o["form ❌"] = form);
    o.fnClass = typeof (fnClass ?? "basic") == "string" ? funcClass.enums[fnClass] : fnClass;
    if (!o.fnClass) { throw new TypeError(`not a function fnClass: ${o.fnClass ?? fnClass}`)}
    fnClass = funcClass(f);
    eq(o.fnClass, fnClass) || (o["fnClass ❌"] = fnClass);
    Object.defineProperty(o, Symbol.toStringTag, {get: strTag})
    return o;
  });
}4f:[]
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funcForm.enums.native),\n  unknown: typer(\"arrow function\", o => (typeof o === \"function\") && funcForm(o) === funcForm.enums.unknown)\n}).map(([key, value]) => [key, {enumerable: true, value}]), [Symbol.toStringTag, Object.getOwnPropertyDescriptor(funcForm.enums, Symbol.toStringTag)]]))","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":300,"value":"$4a","pinned":false,"hidden":false,"mode":"md","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"","database":"$undefined"},{"id":62,"value":"$4b","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":34,"value":"funcForm.enums // output values for `funcForm`","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":28,"value":"$4c","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":50,"value":"funcClass.enums // output values for `funcClass`","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":226,"value":"funcClass.classes\n/* {\n  basic: Function,\n  async: AsyncFunction,\n  gen: GeneratorFunction,\n  asyncGen: AsyncGeneratorFunction\n} */","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":453,"value":"## tests","pinned":false,"hidden":false,"mode":"md","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"","database":"$undefined"},{"id":133,"value":"$4d","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":455,"value":"## appendix","pinned":false,"hidden":false,"mode":"md","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"","database":"$undefined"},{"id":110,"value":"$4e","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":174,"value":"import {inspect} from \"@rmw4269/inspect\"","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":6,"value":"import {typer, like as likeSrc, func as funcSrc, makeNull, style} from \"@rmw4269/interfaces\"","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":9,"value":"Acorn = Object.defineProperty(await require(\"acorn@8.8/dist/acorn.js\"), Symbol.toStringTag, {value: \"Acorn\"})","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":368,"value":"style","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":373,"value":"cellWidth","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":370,"value":"import {cellWidth} from \"@rmw4269/css-cell-width\"","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"}],"files":"$W4f","stdlib":"1"}}
45:"$44:body"

interfaces for function types

func type functions

`func` type functions