Add JSON to TypeScript script

Scripts/JSONtoTypeScript.js

@@ -0,0 +1,235 @@
+/**
+	{
+		"api":1,
+		"name":"JSON to TypeScript",
+		"description":"Generates TypeScript interfaces from a JSON document.",
+		"author":"S4nshine",
+		"icon":"metamorphose",
+		"tags":"json,typescript,ts,type,types,interface,convert"
+	}
+**/
+
+const ROOT_NAME = "Root";
+const INDENT = "  ";
+const IDENTIFIER = /^[A-Za-z_$][A-Za-z0-9_$]*$/;
+
+let declarations = [];
+let usedNames = Object.create(null);
+
+function main(state) {
+
+	const input = state.text;
+
+	if (!input || input.trim().length === 0) {
+		state.postError("Nothing to convert.");
+		return;
+	}
+
+	let parsed;
+
+	try {
+		parsed = JSON.parse(input);
+	} catch (error) {
+		state.postError("Invalid JSON: " + error.message);
+		return;
+	}
+
+	// The script's VM is kept alive between runs, so state has to be reset.
+	declarations = [];
+	usedNames = Object.create(null);
+
+	const rootType = inferUnion([parsed], ROOT_NAME);
+
+	const output = declarations.map(function (declaration) {
+		return "interface " + declaration.name + " {\n" + declaration.body + "\n}";
+	});
+
+	// Arrays, primitives and unions can't be an interface, so they get an alias.
+	if (declarations.length === 0 || rootType !== declarations[0].name) {
+		output.unshift("type " + uniqueName(ROOT_NAME) + " = " + rootType + ";");
+	}
+
+	state.text = output.join("\n\n");
+
+	const count = declarations.length;
+	state.postInfo(count === 0 ? "Type alias generated"
+		: count === 1 ? "1 interface generated"
+		: count + " interfaces generated");
+}
+
+/**
+ * Returns the type of every value a single key (or array slot) was seen holding.
+ * Objects are merged into one interface rather than becoming a union, so that
+ * an array of similar records produces a single, useful type.
+ */
+function inferUnion(values, suggestedName) {
+
+	const objects = [];
+	const arrays = [];
+	const primitives = [];
+	let nullable = false;
+
+	values.forEach(function (value) {
+		if (value === null) {
+			nullable = true;
+		} else if (Array.isArray(value)) {
+			arrays.push(value);
+		} else if (typeof value === "object") {
+			objects.push(value);
+		} else if (primitives.indexOf(typeof value) === -1) {
+			primitives.push(typeof value);
+		}
+	});
+
+	const parts = [];
+
+	if (objects.length > 0) {
+		parts.push(declareInterface(objects, suggestedName));
+	}
+
+	if (arrays.length > 0) {
+		parts.push(inferArrayType(arrays, suggestedName));
+	}
+
+	primitives.forEach(function (primitive) {
+		parts.push(primitive);
+	});
+
+	if (nullable) {
+		parts.push("null");
+	}
+
+	if (parts.length === 0) {
+		return "unknown";
+	}
+
+	return parts.join(" | ");
+}
+
+/**
+ * Flattens every array seen for a key into a single element type, so that
+ * [[1], [2, 3]] describes number[][] rather than two competing shapes.
+ */
+function inferArrayType(arrays, suggestedName) {
+
+	const elements = [];
+
+	arrays.forEach(function (array) {
+		array.forEach(function (element) {
+			elements.push(element);
+		});
+	});
+
+	if (elements.length === 0) {
+		return "unknown[]";
+	}
+
+	const elementType = inferUnion(elements, singularize(suggestedName));
+
+	return elementType.indexOf(" | ") === -1 ? elementType + "[]" : "(" + elementType + ")[]";
+}
+
+/**
+ * Builds one interface out of every object sample seen in the same position.
+ * A key missing from any of the samples is marked optional.
+ */
+function declareInterface(samples, suggestedName) {
+
+	const keys = [];
+	const seen = Object.create(null);
+
+	samples.forEach(function (sample) {
+		Object.keys(sample).forEach(function (key) {
+			if (!seen[key]) {
+				seen[key] = true;
+				keys.push(key);
+			}
+		});
+	});
+
+	if (keys.length === 0) {
+		return "Record<string, unknown>";
+	}
+
+	// The slot is claimed before recursing so that parents are declared
+	// above their children in the output.
+	const slot = declarations.length;
+	declarations.push(null);
+	const name = uniqueName(suggestedName);
+
+	const body = keys.map(function (key) {
+
+		const present = samples.filter(function (sample) {
+			return Object.prototype.hasOwnProperty.call(sample, key);
+		});
+
+		const optional = present.length < samples.length;
+
+		const type = inferUnion(present.map(function (sample) {
+			return sample[key];
+		}), pascalCase(key));
+
+		return INDENT + formatKey(key) + (optional ? "?" : "") + ": " + type + ";";
+
+	}).join("\n");
+
+	declarations[slot] = { name: name, body: body };
+
+	return name;
+}
+
+function formatKey(key) {
+	return IDENTIFIER.test(key) ? key : JSON.stringify(key);
+}
+
+function pascalCase(text) {
+
+	const name = String(text)
+		.split(/[^A-Za-z0-9]+/)
+		.filter(function (word) { return word.length > 0; })
+		.map(function (word) { return word.charAt(0).toUpperCase() + word.slice(1); })
+		.join("");
+
+	if (name.length === 0) {
+		return "Value";
+	}
+
+	return /^[0-9]/.test(name) ? "_" + name : name;
+}
+
+function singularize(name) {
+
+	if (/ies$/.test(name)) {
+		return name.replace(/ies$/, "y");
+	}
+
+	if (/(ch|sh|ss|x|z)es$/.test(name)) {
+		return name.replace(/es$/, "");
+	}
+
+	// "Status", "Address" and "Analysis" are singular already.
+	if (/(us|ss|is)$/.test(name)) {
+		return name + "Item";
+	}
+
+	if (/s$/.test(name)) {
+		return name.replace(/s$/, "");
+	}
+
+	return name + "Item";
+}
+
+function uniqueName(base) {
+
+	let name = base;
+	let counter = 2;
+
+	while (usedNames[name]) {
+		name = base + counter;
+		counter++;
+	}
+
+	usedNames[name] = true;
+
+	return name;
+}