Merge pull request #36 from proj4js/eslint-es2015

Use eslint to enforce ES2015 features

Author: ahocevar

.eslintrc

@@ -5,7 +5,7 @@ class PROJJSONBuilder2015 extends PROJJSONBuilderBase {
     super.convert(node, result);
 
     // Skip `CS` and `USAGE` nodes for WKT2-2015
-    if (result.coordinate_system?.subtype === "Cartesian") {
+    if (result.coordinate_system && result.coordinate_system.subtype === 'Cartesian') {
       delete result.coordinate_system;
     }
     if (result.usage) {

PROJJSONBuilder2015.js

@@ -5,7 +5,7 @@ class PROJJSONBuilder2019 extends PROJJSONBuilderBase {
     super.convert(node, result);
 
     // Handle `CS` node for WKT2-2019
-    const csNode = node.find((child) => Array.isArray(child) && child[0] === "CS");
+    const csNode = node.find((child) => Array.isArray(child) && child[0] === 'CS');
     if (csNode) {
       result.coordinate_system = {
         subtype: csNode[1],
@@ -14,13 +14,21 @@ class PROJJSONBuilder2019 extends PROJJSONBuilderBase {
     }
 
     // Handle `USAGE` node for WKT2-2019
-    const usageNode = node.find((child) => Array.isArray(child) && child[0] === "USAGE");
+    const usageNode = node.find((child) => Array.isArray(child) && child[0] === 'USAGE');
     if (usageNode) {
-      result.usage = {
-        scope: usageNode.find((child) => Array.isArray(child) && child[0] === "SCOPE")?.[1],
-        area: usageNode.find((child) => Array.isArray(child) && child[0] === "AREA")?.[1],
-        bbox: usageNode.find((child) => Array.isArray(child) && child[0] === "BBOX")?.slice(1),
-      };
+      const scope = usageNode.find((child) => Array.isArray(child) && child[0] === 'SCOPE');
+      const area = usageNode.find((child) => Array.isArray(child) && child[0] === 'AREA');
+      const bbox = usageNode.find((child) => Array.isArray(child) && child[0] === 'BBOX');
+      result.usage = {};
+      if (scope) {
+        result.usage.scope = scope[1];
+      }
+      if (area) {
+        result.usage.area = area[1];
+      }
+      if (bbox) {
+        result.usage.bbox = bbox.slice(1);
+      }
     }
 
     return result;