Supports for Optional chaining & Nullish coalescing

package.json

@@ -28,6 +28,7 @@
     "rimraf": "^3.0.0",
     "rollup": "^1.25.0",
     "rollup-plugin-sourcemaps": "^0.4.2",
+    "semver": "^7.3.2",
     "vuepress": "^1.2.0",
     "warun": "^1.0.0"
   },

src/get-static-value.js

@@ -251,23 +251,34 @@ const operations = Object.freeze({
         if (args != null) {
             if (calleeNode.type === "MemberExpression") {
                 const object = getStaticValueR(calleeNode.object, initialScope)
-                const property = calleeNode.computed
-                    ? getStaticValueR(calleeNode.property, initialScope)
-                    : { value: calleeNode.property.name }
-
-                if (object != null && property != null) {
-                    const receiver = object.value
-                    const methodName = property.value
-                    if (callAllowed.has(receiver[methodName])) {
-                        return { value: receiver[methodName](...args) }
+                if (object != null) {
+                    if (
+                        object.value == null &&
+                        (object.optional || node.optional)
+                    ) {
+                        return { value: undefined, optional: true }
                     }
-                    if (callPassThrough.has(receiver[methodName])) {
-                        return { value: args[0] }
+                    const property = calleeNode.computed
+                        ? getStaticValueR(calleeNode.property, initialScope)
+                        : { value: calleeNode.property.name }
+
+                    if (property != null) {
+                        const receiver = object.value
+                        const methodName = property.value
+                        if (callAllowed.has(receiver[methodName])) {
+                            return { value: receiver[methodName](...args) }
+                        }
+                        if (callPassThrough.has(receiver[methodName])) {
+                            return { value: args[0] }
+                        }
                     }
                 }
             } else {
                 const callee = getStaticValueR(calleeNode, initialScope)
                 if (callee != null) {
+                    if (callee.value == null && node.optional) {
+                        return { value: undefined, optional: true }
+                    }
                     const func = callee.value
                     if (callAllowed.has(func)) {
                         return { value: func(...args) }
@@ -340,7 +351,8 @@ const operations = Object.freeze({
         if (left != null) {
             if (
                 (node.operator === "||" && Boolean(left.value) === true) ||
-                (node.operator === "&&" && Boolean(left.value) === false)
+                (node.operator === "&&" && Boolean(left.value) === false) ||
+                (node.operator === "??" && left.value != null)
             ) {
                 return left
             }
@@ -356,16 +368,25 @@ const operations = Object.freeze({
 
     MemberExpression(node, initialScope) {
         const object = getStaticValueR(node.object, initialScope)
-        const property = node.computed
-            ? getStaticValueR(node.property, initialScope)
-            : { value: node.property.name }
-
-        if (
-            object != null &&
-            property != null &&
-            !isGetter(object.value, property.value)
-        ) {
-            return { value: object.value[property.value] }
+        if (object != null) {
+            if (object.value == null && (object.optional || node.optional)) {
+                return { value: undefined, optional: true }
+            }
+            const property = node.computed
+                ? getStaticValueR(node.property, initialScope)
+                : { value: node.property.name }
+
+            if (property != null && !isGetter(object.value, property.value)) {
+                return { value: object.value[property.value] }
+            }
+        }
+        return null
+    },
+
+    ChainExpression(node, initialScope) {
+        const expression = getStaticValueR(node.expression, initialScope)
+        if (expression != null) {
+            return { value: expression.value }
         }
         return null
     },
@@ -493,7 +514,7 @@ const operations = Object.freeze({
  * Get the value of a given node if it's a static value.
  * @param {Node} node The node to get.
  * @param {Scope|undefined} initialScope The scope to start finding variable.
- * @returns {{value:any}|null} The static value of the node, or `null`.
+ * @returns {{value:any}|{value:undefined,optional?:true}|null} The static value of the node, or `null`.
  */
 function getStaticValueR(node, initialScope) {
     if (node != null && Object.hasOwnProperty.call(operations, node.type)) {
@@ -506,7 +527,7 @@ function getStaticValueR(node, initialScope) {
  * Get the value of a given node if it's a static value.
  * @param {Node} node The node to get.
  * @param {Scope} [initialScope] The scope to start finding variable. Optional. If this scope was given, this tries to resolve identifier references which are in the given node as much as possible.
- * @returns {{value:any}|null} The static value of the node, or `null`.
+ * @returns {{value:any}|{value:undefined,optional?:true}|null} The static value of the node, or `null`.
  */
 export function getStaticValue(node, initialScope = null) {
     try {

src/has-side-effect.js

@@ -23,6 +23,16 @@ const typeConversionBinaryOps = Object.freeze(
     ])
 )
 const typeConversionUnaryOps = Object.freeze(new Set(["-", "+", "!", "~"]))
+
+/**
+ * Check whether the given value is an ASTNode or not.
+ * @param {any} x The value to check.
+ * @returns {boolean} `true` if the value is an ASTNode.
+ */
+function isNode(x) {
+    return x !== null && typeof x === "object" && typeof x.type === "string"
+}
+
 const visitor = Object.freeze(
     Object.assign(Object.create(null), {
         $visit(node, options, visitorKeys) {
@@ -44,13 +54,16 @@ const visitor = Object.freeze(
                 if (Array.isArray(value)) {
                     for (const element of value) {
                         if (
-                            element &&
+                            isNode(element) &&
                             this.$visit(element, options, visitorKeys)
                         ) {
                             return true
                         }
                     }
-                } else if (value && this.$visit(value, options, visitorKeys)) {
+                } else if (
+                    isNode(value) &&
+                    this.$visit(value, options, visitorKeys)
+                ) {
                     return true
                 }
             }

src/reference-tracker.js

@@ -41,6 +41,8 @@ function isPassThrough(node) {
             return true
         case "SequenceExpression":
             return parent.expressions[parent.expressions.length - 1] === node
+        case "ChainExpression":
+            return true
 
         default:
             return false

test/get-static-value.js

@@ -1,5 +1,6 @@
 import assert from "assert"
 import eslint from "eslint"
+import semver from "semver"
 import { getStaticValue } from "../src/"
 
 describe("The 'getStaticValue' function", () => {
@@ -143,6 +144,102 @@ const aMap = Object.freeze({
             code: "RegExp.$1",
             expected: null,
         },
+        ...(semver.gte(eslint.CLIEngine.version, "6.0.0")
+            ? [
+                  {
+                      code: "const a = null, b = 42; a ?? b",
+                      expected: { value: 42 },
+                  },
+                  {
+                      code: "const a = undefined, b = 42; a ?? b",
+                      expected: { value: 42 },
+                  },
+                  {
+                      code: "const a = false, b = 42; a ?? b",
+                      expected: { value: false },
+                  },
+                  {
+                      code: "const a = 42, b = null; a ?? b",
+                      expected: { value: 42 },
+                  },
+                  {
+                      code: "const a = 42, b = undefined; a ?? b",
+                      expected: { value: 42 },
+                  },
+                  {
+                      code: "const a = { b: { c: 42 } }; a?.b?.c",
+                      expected: { value: 42 },
+                  },
+                  {
+                      code: "const a = { b: { c: 42 } }; a?.b?.['c']",
+                      expected: { value: 42 },
+                  },
+                  {
+                      code: "const a = { b: null }; a?.b?.c",
+                      expected: { value: undefined },
+                  },
+                  {
+                      code: "const a = { b: undefined }; a?.b?.c",
+                      expected: { value: undefined },
+                  },
+                  {
+                      code: "const a = { b: null }; a?.b?.['c']",
+                      expected: { value: undefined },
+                  },
+                  {
+                      code: "const a = null; a?.b?.c",
+                      expected: { value: undefined },
+                  },
+                  {
+                      code: "const a = null; a?.b.c",
+                      expected: { value: undefined },
+                  },
+                  {
+                      code: "const a = void 0; a?.b.c",
+                      expected: { value: undefined },
+                  },
+                  {
+                      code: "const a = { b: { c: 42 } }; (a?.b).c",
+                      expected: { value: 42 },
+                  },
+                  {
+                      code: "const a = null; (a?.b).c",
+                      expected: null,
+                  },
+                  {
+                      code: "const a = { b: null }; (a?.b).c",
+                      expected: null,
+                  },
+                  {
+                      code: "const a = { b: { c: String } }; a?.b?.c?.(42)",
+                      expected: { value: "42" },
+                  },
+                  {
+                      code: "const a = null; a?.b?.c?.(42)",
+                      expected: { value: undefined },
+                  },
+                  {
+                      code: "const a = { b: { c: String } }; a?.b.c(42)",
+                      expected: { value: "42" },
+                  },
+                  {
+                      code: "const a = null; a?.b.c(42)",
+                      expected: { value: undefined },
+                  },
+                  {
+                      code: "null?.()",
+                      expected: { value: undefined },
+                  },
+                  {
+                      code: "const a = null; a?.()",
+                      expected: { value: undefined },
+                  },
+                  {
+                      code: "a?.()",
+                      expected: null,
+                  },
+              ]
+            : []),
     ]) {
         it(`should return ${JSON.stringify(expected)} from ${code}`, () => {
             const linter = new eslint.Linter()
@@ -158,7 +255,11 @@ const aMap = Object.freeze({
             }))
             linter.verify(code, {
                 env: { es6: true },
-                parserOptions: { ecmaVersion: 2018 },
+                parserOptions: {
+                    ecmaVersion: semver.gte(eslint.CLIEngine.version, "6.0.0")
+                        ? 2020
+                        : 2018,
+                },
                 rules: { test: "error" },
             })
 

test/has-side-effect.js

@@ -1,5 +1,6 @@
 import assert from "assert"
 import eslint from "eslint"
+import semver from "semver"
 import dp from "dot-prop"
 import { hasSideEffect } from "../src/"
 
@@ -46,11 +47,29 @@ describe("The 'hasSideEffect' function", () => {
             options: undefined,
             expected: true,
         },
+        ...(semver.gte(eslint.CLIEngine.version, "6.0.0")
+            ? [
+                  {
+                      code: "f?.()",
+                      options: undefined,
+                      expected: true,
+                  },
+              ]
+            : []),
         {
             code: "a + f()",
             options: undefined,
             expected: true,
         },
+        ...(semver.gte(eslint.CLIEngine.version, "6.0.0")
+            ? [
+                  {
+                      code: "a + f?.()",
+                      options: undefined,
+                      expected: true,
+                  },
+              ]
+            : []),
         {
             code: "obj.a",
             options: undefined,
@@ -61,6 +80,20 @@ describe("The 'hasSideEffect' function", () => {
             options: { considerGetters: true },
             expected: true,
         },
+        ...(semver.gte(eslint.CLIEngine.version, "6.0.0")
+            ? [
+                  {
+                      code: "obj?.a",
+                      options: undefined,
+                      expected: false,
+                  },
+                  {
+                      code: "obj?.a",
+                      options: { considerGetters: true },
+                      expected: true,
+                  },
+              ]
+            : []),
         {
             code: "obj[a]",
             options: undefined,
@@ -76,6 +109,25 @@ describe("The 'hasSideEffect' function", () => {
             options: { considerImplicitTypeConversion: true },
             expected: true,
         },
+        ...(semver.gte(eslint.CLIEngine.version, "6.0.0")
+            ? [
+                  {
+                      code: "obj?.[a]",
+                      options: undefined,
+                      expected: false,
+                  },
+                  {
+                      code: "obj?.[a]",
+                      options: { considerGetters: true },
+                      expected: true,
+                  },
+                  {
+                      code: "obj?.[a]",
+                      options: { considerImplicitTypeConversion: true },
+                      expected: true,
+                  },
+              ]
+            : []),
         {
             code: "obj[0]",
             options: { considerImplicitTypeConversion: true },
@@ -242,7 +294,11 @@ describe("The 'hasSideEffect' function", () => {
             }))
             const messages = linter.verify(code, {
                 env: { es6: true },
-                parserOptions: { ecmaVersion: 2018 },
+                parserOptions: {
+                    ecmaVersion: semver.gte(eslint.CLIEngine.version, "6.0.0")
+                        ? 2020
+                        : 2018,
+                },
                 rules: { test: "error" },
             })