Format property names consistently

package.json

@@ -8,6 +8,7 @@
   "dependencies": {
     "ast-types": "git+https://github.com/jlongster/ast-types.git",
     "babylon": "^6.15.0",
+    "esutils": "^2.0.2",
     "flow-parser": "^0.37.0",
     "minimist": "^1.2.0",
     "private": "^0.1.6",

src/printer.js

@@ -25,6 +25,7 @@ var isString = types.builtInTypes.string;
 var isObject = types.builtInTypes.object;
 var FastPath = require("./fast-path");
 var util = require("./util");
+var isIdentifierName = require("esutils").keyword.isIdentifierNameES6;
 
 function PrintResult(code, sourceMap) {
   assert.ok(this instanceof PrintResult);
@@ -641,13 +642,14 @@ function genericPrintNoParens(path, options, print) {
       return printMethod(path, options, print);
     }
 
-    if (n.computed) {
-      parts.push("[", path.call(print, "key"), "]");
+    if (n.shorthand) {
+      parts.push(path.call(print, "value"));
     } else {
-      parts.push(path.call(print, n.shorthand ? "value" : "key"));
-    }
-
-    if (!n.shorthand) {
+      if (n.computed) {
+        parts.push("[", path.call(print, "key"), "]");
+      } else {
+        parts.push(printPropertyKey(path, print));
+      }
       parts.push(": ", path.call(print, "value"));
     }
 
@@ -1155,15 +1157,18 @@ function genericPrintNoParens(path, options, print) {
     if (n.static)
       parts.push("static ");
 
-    var key = path.call(print, "key");
+    var key;
 
     if (n.computed) {
-      key = concat([ "[", key, "]" ]);
-    } else if (n.variance === "plus") {
-      key = concat([ "+", key ]);
-    } else if (n.variance === "minus") {
-      key = concat([ "-", key ]);
-    }
+      key = concat([ "[", path.call(print, "key"), "]" ]);
+    } else {
+      key = printPropertyKey(path, print);
+      if (n.variance === "plus") {
+        key = concat([ "+", key ]);
+      } else if (n.variance === "minus") {
+        key = concat([ "-", key ]);
+      }
+    } 
 
     parts.push(key);
 
@@ -1608,6 +1613,21 @@ function printStatementSequence(path, options, print) {
   return join(hardline, printed);
 }
 
+function printPropertyKey(path, print) {
+  var node = path.getNode().key;
+  if (node.type === "StringLiteral") {
+    if (isIdentifierName(node.value)) { // 'a' -> a
+      return node.value;
+    }
+    let val = parseFloat(node.value);
+    let strVal = fromString(val);
+    if (val >= 0 && strVal === node.value) { // '0' -> 0
+      return strVal;
+    }
+  }
+  return path.call(print, "key");
+}
+
 function printMethod(path, options, print) {
   var node = path.getNode();
   var kind = node.kind;
@@ -1633,7 +1653,7 @@ function printMethod(path, options, print) {
     parts.push(kind, " ");
   }
 
-  var key = path.call(print, "key");
+  var key = printPropertyKey(path, print);
 
   if (node.computed) {
     key = concat([ "[", key, "]" ]);
@@ -1773,7 +1793,7 @@ function printObjectMethod(path, options, print) {
     return printMethod(path, options, print);
   }
 
-  var key = path.call(print, "key");
+  var key = printPropertyKey(path, print);
 
   if (objMethod.computed) {
     parts.push("[", key, "]");