Update: add latestEcmaVersion & supportedEcmaVersions

espree.js

@@ -62,6 +62,7 @@ const acorn = require("acorn");
 const jsx = require("acorn-jsx");
 const astNodeTypes = require("./lib/ast-node-types");
 const espree = require("./lib/espree");
+const { latestEcmaVersion, supportedEcmaVersions } = require("./lib/options");
 
 // To initialize lazily.
 const parsers = {
@@ -170,3 +171,7 @@ exports.Syntax = (function() {
 exports.VisitorKeys = (function() {
     return require("eslint-visitor-keys").KEYS;
 }());
+
+exports.latestEcmaVersion = latestEcmaVersion;
+
+exports.supportedEcmaVersions = supportedEcmaVersions;

lib/espree.js

@@ -2,77 +2,11 @@
 
 /* eslint-disable no-param-reassign*/
 const TokenTranslator = require("./token-translator");
+const { normalizeOptions } = require("./options");
 
-const DEFAULT_ECMA_VERSION = 5;
 const STATE = Symbol("espree's internal state");
 const ESPRIMA_FINISH_NODE = Symbol("espree's esprimaFinishNode");
 
-/**
- * Normalize ECMAScript version from the initial config
- * @param {number} ecmaVersion ECMAScript version from the initial config
- * @throws {Error} throws an error if the ecmaVersion is invalid.
- * @returns {number} normalized ECMAScript version
- */
-function normalizeEcmaVersion(ecmaVersion = DEFAULT_ECMA_VERSION) {
-    if (typeof ecmaVersion !== "number") {
-        throw new Error(`ecmaVersion must be a number. Received value of type ${typeof ecmaVersion} instead.`);
-    }
-
-    let version = ecmaVersion;
-
-    // Calculate ECMAScript edition number from official year version starting with
-    // ES2015, which corresponds with ES6 (or a difference of 2009).
-    if (version >= 2015) {
-        version -= 2009;
-    }
-
-    switch (version) {
-        case 3:
-        case 5:
-        case 6:
-        case 7:
-        case 8:
-        case 9:
-        case 10:
-        case 11:
-            return version;
-
-        // no default
-    }
-
-    throw new Error("Invalid ecmaVersion.");
-}
-
-/**
- * Normalize sourceType from the initial config
- * @param {string} sourceType to normalize
- * @throws {Error} throw an error if sourceType is invalid
- * @returns {string} normalized sourceType
- */
-function normalizeSourceType(sourceType = "script") {
-    if (sourceType === "script" || sourceType === "module") {
-        return sourceType;
-    }
-    throw new Error("Invalid sourceType.");
-}
-
-/**
- * Normalize parserOptions
- * @param {Object} options the parser options to normalize
- * @throws {Error} throw an error if found invalid option.
- * @returns {Object} normalized options
- */
-function normalizeOptions(options) {
-    const ecmaVersion = normalizeEcmaVersion(options.ecmaVersion);
-    const sourceType = normalizeSourceType(options.sourceType);
-    const ranges = options.range === true;
-    const locations = options.loc === true;
-
-    if (sourceType === "module" && ecmaVersion < 6) {
-        throw new Error("sourceType 'module' is not supported when ecmaVersion < 2015. Consider adding `{ ecmaVersion: 2015 }` to the parser options.");
-    }
-    return Object.assign({}, options, { ecmaVersion, sourceType, ranges, locations });
-}
 
 /**
  * Converts an Acorn comment to a Esprima comment.

lib/options.js

@@ -0,0 +1,105 @@
+/**
+ * @fileoverview A collection of methods for processing Espree's options.
+ * @author Kai Cataldo
+ */
+
+"use strict";
+
+//------------------------------------------------------------------------------
+// Helpers
+//------------------------------------------------------------------------------
+
+const DEFAULT_ECMA_VERSION = 5;
+const SUPPORTED_VERSIONS = [
+    3,
+    5,
+    6,
+    7,
+    8,
+    9,
+    10,
+    11
+];
+
+/**
+ * Normalize ECMAScript version from the initial config
+ * @param {number} ecmaVersion ECMAScript version from the initial config
+ * @throws {Error} throws an error if the ecmaVersion is invalid.
+ * @returns {number} normalized ECMAScript version
+ */
+function normalizeEcmaVersion(ecmaVersion = DEFAULT_ECMA_VERSION) {
+    if (typeof ecmaVersion !== "number") {
+        throw new Error(`ecmaVersion must be a number. Received value of type ${typeof ecmaVersion} instead.`);
+    }
+
+    let version = ecmaVersion;
+
+    // Calculate ECMAScript edition number from official year version starting with
+    // ES2015, which corresponds with ES6 (or a difference of 2009).
+    if (version >= 2015) {
+        version -= 2009;
+    }
+
+    if (!SUPPORTED_VERSIONS.includes(version)) {
+        throw new Error("Invalid ecmaVersion.");
+    }
+
+    return version;
+}
+
+/**
+ * Normalize sourceType from the initial config
+ * @param {string} sourceType to normalize
+ * @throws {Error} throw an error if sourceType is invalid
+ * @returns {string} normalized sourceType
+ */
+function normalizeSourceType(sourceType = "script") {
+    if (sourceType === "script" || sourceType === "module") {
+        return sourceType;
+    }
+    throw new Error("Invalid sourceType.");
+}
+
+/**
+ * Normalize parserOptions
+ * @param {Object} options the parser options to normalize
+ * @throws {Error} throw an error if found invalid option.
+ * @returns {Object} normalized options
+ */
+function normalizeOptions(options) {
+    const ecmaVersion = normalizeEcmaVersion(options.ecmaVersion);
+    const sourceType = normalizeSourceType(options.sourceType);
+    const ranges = options.range === true;
+    const locations = options.loc === true;
+
+    if (sourceType === "module" && ecmaVersion < 6) {
+        throw new Error("sourceType 'module' is not supported when ecmaVersion < 2015. Consider adding `{ ecmaVersion: 2015 }` to the parser options.");
+    }
+    return Object.assign({}, options, { ecmaVersion, sourceType, ranges, locations });
+}
+
+/**
+ * Get the latest ECMAScript version supported by Espree.
+ * @returns {number} The latest ECMAScript version.
+ */
+function latestEcmaVersion() {
+    return Math.max(...SUPPORTED_VERSIONS);
+}
+
+/**
+ * Get the list of ECMAScript versions supported by Espree.
+ * @returns {number[]} An array containing the supported ECMAScript versions.
+ */
+function supportedEcmaVersions() {
+    return [...SUPPORTED_VERSIONS];
+}
+
+//------------------------------------------------------------------------------
+// Public
+//------------------------------------------------------------------------------
+
+module.exports = {
+    normalizeOptions,
+    latestEcmaVersion,
+    supportedEcmaVersions
+};

tests/lib/supported-ecmaversions.js

@@ -0,0 +1,40 @@
+/**
+ * @fileoverview Tests for latestEcmaVersion() & supportedEcmaVersions().
+ * @author Kai Cataldo
+ */
+
+"use strict";
+
+//------------------------------------------------------------------------------
+// Requirements
+//------------------------------------------------------------------------------
+
+const assert = require("assert"),
+    espree = require("../../espree");
+
+//------------------------------------------------------------------------------
+// Tests
+//------------------------------------------------------------------------------
+
+describe("latestEcmaVersion()", () => {
+    it("should return the latest supported ecmaVersion", () => {
+        assert.strictEqual(espree.latestEcmaVersion(), 11);
+    });
+});
+
+describe("supportedEcmaVersions()", () => {
+    it("should return an array of all supported versions", () => {
+        assert.deepStrictEqual(
+            espree.supportedEcmaVersions(),
+            [3, 5, 6, 7, 8, 9, 10, 11]
+        );
+    });
+
+    it("the array of supported versions should not be mutable by reference", () => {
+        const supportedVersions = espree.supportedEcmaVersions();
+        const originalValue = [...supportedVersions];
+
+        supportedVersions.push("a", "b", "c");
+        assert.deepStrictEqual(espree.supportedEcmaVersions(), originalValue);
+    });
+});