Quote and unquote number keys

changelog_unreleased/javascript/pr-8508.md

@@ -0,0 +1,26 @@
+#### Quote and unquote number keys ([#8508](https://github.com/prettier/prettier/pull/8508) by [@lydell](https://github.com/lydell))
+
+Prettier removes quotes from object keys if they are identifiers. Now, Prettier also removes quotes from object keys that are numbers.
+
+If you use `quoteProps: "consistent"`, Prettier can also _add_ quotes to number keys so that _all_ properties end up with quotes.
+
+<!-- prettier-ignore -->
+```jsx
+// Input
+x = {
+  "a": null,
+  "1": null,
+};
+
+// Prettier stable
+x = {
+  a: null,
+  "1": null,
+};
+
+// Prettier master
+x = {
+  a: null,
+  1: null,
+};
+```

src/language-js/clean.js

@@ -89,6 +89,7 @@ function clean(ast, newObj, parent) {
     typeof ast.key === "object" &&
     ast.key &&
     (ast.key.type === "Literal" ||
+      ast.key.type === "NumericLiteral" ||
       ast.key.type === "StringLiteral" ||
       ast.key.type === "Identifier")
   ) {

src/language-js/printer-estree.js

@@ -68,12 +68,13 @@ const {
   isMemberExpressionChain,
   isMemberish,
   isNgForOf,
+  isNumericLiteral,
   isObjectType,
   isObjectTypePropertyAFunction,
   isSimpleFlowType,
   isSimpleTemplateLiteral,
   isStringLiteral,
-  isStringPropSafeToCoerceToIdentifier,
+  isStringPropSafeToUnquote,
   isTemplateOnItsOwnLine,
   isTestCall,
   isTheOnlyJSXElementInMarkdown,
@@ -3733,33 +3734,47 @@ function printPropertyKey(path, options, print) {
       (prop) =>
         !prop.computed &&
         prop.key &&
-        isStringLiteral(prop.key) &&
-        !isStringPropSafeToCoerceToIdentifier(prop, options)
+        ((isStringLiteral(prop.key) &&
+          !isStringPropSafeToUnquote(prop, options)) ||
+          (isNumericLiteral(prop.key) &&
+            (options.parser === "flow" || options.parser === "babel-flow")))
     );
     needsQuoteProps.set(parent, objectHasStringProp);
   }
 
   if (
-    key.type === "Identifier" &&
+    (key.type === "Identifier" || isNumericLiteral(key)) &&
     (options.parser === "json" ||
       (options.quoteProps === "consistent" && needsQuoteProps.get(parent)))
   ) {
     // a -> "a"
-    const prop = printString(JSON.stringify(key.name), options);
+    // 1e2 -> "100"
+    const prop = printString(
+      JSON.stringify(
+        key.type === "Identifier" ? key.name : key.value.toString()
+      ),
+      options
+    );
     return path.call(
       (keyPath) => comments.printComments(keyPath, () => prop, options),
       "key"
     );
   }
 
   if (
-    isStringPropSafeToCoerceToIdentifier(node, options) &&
+    isStringPropSafeToUnquote(node, options) &&
     (options.quoteProps === "as-needed" ||
       (options.quoteProps === "consistent" && !needsQuoteProps.get(parent)))
   ) {
     // 'a' -> a
+    // '1e+100' -> 1e100
     return path.call(
-      (keyPath) => comments.printComments(keyPath, () => key.value, options),
+      (keyPath) =>
+        comments.printComments(
+          keyPath,
+          () => (/^\d/.test(key.value) ? printNumber(key.value) : key.value),
+          options
+        ),
       "key"
     );
   }

src/language-js/utils.js

@@ -734,18 +734,20 @@ function returnArgumentHasLeadingComment(options, argument) {
   return false;
 }
 
-function isStringPropSafeToCoerceToIdentifier(node, options) {
+function isStringPropSafeToUnquote(node, options) {
   return (
+    options.parser !== "json" &&
     isStringLiteral(node.key) &&
-    isIdentifierName(node.key.value) &&
     rawText(node.key).slice(1, -1) === node.key.value &&
-    options.parser !== "json" &&
-    // With `--strictPropertyInitialization`, TS treats properties with quoted names differently than unquoted ones.
-    // See https://github.com/microsoft/TypeScript/pull/20075
-    !(
-      (options.parser === "typescript" || options.parser === "babel-ts") &&
-      node.type === "ClassProperty"
-    )
+    ((isIdentifierName(node.key.value) &&
+      // With `--strictPropertyInitialization`, TS treats properties with quoted names differently than unquoted ones.
+      // See https://github.com/microsoft/TypeScript/pull/20075
+      !(
+        (options.parser === "typescript" || options.parser === "babel-ts") &&
+        node.type === "ClassProperty"
+      )) ||
+      (String(Number(node.key.value)) === node.key.value &&
+        !(options.parser === "flow" || options.parser === "babel-flow")))
   );
 }
 
@@ -1103,7 +1105,7 @@ module.exports = {
   isSimpleFlowType,
   isSimpleTemplateLiteral,
   isStringLiteral,
-  isStringPropSafeToCoerceToIdentifier,
+  isStringPropSafeToUnquote,
   isTemplateOnItsOwnLine,
   isTestCall,
   isTheOnlyJSXElementInMarkdown,