refactor: Move some ast decisions to their own module

Author: freaktechnik

package-lock.json

@@ -15,7 +15,7 @@
     "@freaktechnik/eslint-config-test": "^5.2.1",
     "ava": "^0.23.0",
     "codecov": "^3.0.0",
-    "eslint": "^4.9.0",
+    "eslint": "^4.10.0",
     "eslint-ava-rule-tester": "^2.0.2",
     "eslint-plugin-eslint-plugin": "^1.2.0",
     "nyc": "^11.3.0"

package.json

@@ -4,6 +4,13 @@
  */
 "use strict";
 
+const {
+    isMethod,
+    getParent,
+    isOnObject
+} = require("../lib/helpers/call-expression");
+const { ARROW_FUNCTION_EXPRESSION } = require("../lib/type");
+
 module.exports = {
     meta: {
         docs: {
@@ -16,13 +23,13 @@ module.exports = {
     create(context) {
         return {
             "CallExpression:exit"(node) {
-                if(!node.callee || node.callee.type !== "MemberExpression" || node.callee.property.name !== "map") {
+                if(!isMethod(node, "map")) {
                     return;
                 }
                 const { callee } = node,
-                    { object: parent } = callee;
+                    parent = getParent(node);
 
-                if(!parent.callee || parent.callee.type !== "MemberExpression" || parent.callee.property.name !== "from" || !parent.callee.object || parent.callee.object.type !== "Identifier" || parent.callee.object.name !== "Array") {
+                if(!isMethod(parent, "from") || !isOnObject(parent, "Array")) {
                     return;
                 }
 
@@ -56,7 +63,7 @@ module.exports = {
                                 paramString = params.map((p) => p.name).join(PARAM_SEPARATOR),
                                 getCallback = (cbk, targ, ps) => {
                                     const source = `(${sourceCode.getText(cbk)})`;
-                                    if(targ && cbk.type !== "ArrowFunctionExpression") {
+                                    if(targ && cbk.type !== ARROW_FUNCTION_EXPRESSION) {
                                         return `${source}.call(${targ.name}${PARAM_SEPARATOR}${ps})`;
                                     }
                                     return `${source}(${ps})`;
@@ -67,7 +74,7 @@ module.exports = {
                             let functionStart = `(${paramString}) => `,
                                 functionEnd = "",
                                 restParamString = '';
-                            if(thisArg && callback.type !== "ArrowFunctionExpression") {
+                            if(thisArg && callback.type !== ARROW_FUNCTION_EXPRESSION) {
                                 functionStart = `function(${paramString}) { return `;
                                 functionEnd = "; }";
                             }

rules/from-map.js

@@ -4,6 +4,12 @@
  */
 "use strict";
 
+const {
+    isMethod,
+    isOnObject
+} = require("../lib/helpers/call-expression");
+const { ARROW_FUNCTION_EXPRESSION } = require("../lib/type");
+
 const arrayFunctions = {
         from: 3
     },
@@ -20,9 +26,10 @@ const arrayFunctions = {
     METHOD_ARG = 2,
     POS_TO_ARRAY = 1,
     FUNC_POS = -2,
-    checkFunction = (node, functionName, argumentPosition) => !node.callee || node.callee.type !== "MemberExpression" || node.callee.property.name !== functionName || node.arguments.length < argumentPosition || node.arguments[argumentPosition + FUNC_POS].type !== "ArrowFunctionExpression",
+    //TODO should also check if the identifier is not an arrow function expression. Similar problem to array detection.
+    checkFunction = (node, functionName, argumentPosition) => !isMethod(node, functionName) || node.arguments.length < argumentPosition || node.arguments[argumentPosition + FUNC_POS].type !== ARROW_FUNCTION_EXPRESSION,
     checkArrayFunction = (functionName, paramPosition, node, context) => {
-        if(checkFunction(node, functionName, paramPosition) || node.callee.object.name !== "Array") {
+        if(checkFunction(node, functionName, paramPosition) || !isOnObject(node, "Array")) {
             return;
         }
         const argument = node.arguments[paramPosition - POS_TO_ARRAY];