Quote and unquote number keys

changelog_unreleased/javascript/pr-8508.md

@@ -24,3 +24,19 @@ x = {
   1: null,
 };
 ```
+
+Note that Prettier only touches “simple” numbers such as `1` and `123.5`. It _won’t_ make the following transformations, as they feel unexpected:
+
+```
+1e2 -> "100"
+0b10 -> "10"
+1_000 -> "1000"
+1.0 -> "1"
+0.99999999999999999 -> "1"
+999999999999999999999 -> "1e+21"
+2n -> "2"
+
+"1e+100" -> 1e+100
+```
+
+(As a side note, please don’t use confusing numbers as object keys!)

src/language-js/printer-estree.js

@@ -72,6 +72,7 @@ const {
   isObjectType,
   isObjectTypePropertyAFunction,
   isSimpleFlowType,
+  isSimpleNumber,
   isSimpleTemplateLiteral,
   isStringLiteral,
   isStringPropSafeToUnquote,
@@ -3742,22 +3743,20 @@ function printPropertyKey(path, options, print) {
 
   if (
     (key.type === "Identifier" ||
-      ((isNumericLiteral(key) || key.type === "BigIntLiteral") &&
+      (isNumericLiteral(key) &&
+        isSimpleNumber(rawText(key)) &&
+        // Avoid converting 999999999999999999999 to 1e+21, 0.99999999999999999 to 1 and 1.0 to 1.
+        String(key.value) === rawText(key) &&
         !(options.parser === "typescript" || options.parser === "babel-ts"))) &&
     (options.parser === "json" ||
       (options.quoteProps === "consistent" && needsQuoteProps.get(parent)))
   ) {
     // a -> "a"
-    // 1e2 -> "100"
-    // 2n -> "2"
-    // 0b10n -> "2"
+    // 1 -> "1"
+    // 1.5 -> "1.5"
     const prop = printString(
       JSON.stringify(
-        key.type === "Identifier"
-          ? key.name
-          : key.type === "BigIntLiteral"
-          ? BigInt(key.value).toString()
-          : key.value.toString()
+        key.type === "Identifier" ? key.name : key.value.toString()
       ),
       options
     );
@@ -3773,7 +3772,8 @@ function printPropertyKey(path, options, print) {
       (options.quoteProps === "consistent" && !needsQuoteProps.get(parent)))
   ) {
     // 'a' -> a
-    // '1e+100' -> 1e100
+    // '1' -> 1
+    // '1.5' -> 1.5
     return path.call(
       (keyPath) =>
         comments.printComments(

src/language-js/utils.js

@@ -765,7 +765,7 @@ function isStringPropSafeToUnquote(node, options) {
         (options.parser === "typescript" || options.parser === "babel-ts") &&
         node.type === "ClassProperty"
       )) ||
-      (!node.key.value.startsWith("-") &&
+      (isSimpleNumber(node.key.value) &&
         String(Number(node.key.value)) === node.key.value &&
         !(
           options.parser === "flow" ||
@@ -776,6 +776,11 @@ function isStringPropSafeToUnquote(node, options) {
   );
 }
 
+// Matches “simple” numbers like `123` and `2.5` but not `1_000`, `1e+100` or `0b10`.
+function isSimpleNumber(numberString) {
+  return /^(\d+|\d+\.\d+)$/.test(numberString);
+}
+
 function isJestEachTemplateLiteral(node, parentNode) {
   /**
    * describe.each`table`(name, fn)
@@ -1128,6 +1133,7 @@ module.exports = {
   isObjectType,
   isObjectTypePropertyAFunction,
   isSimpleFlowType,
+  isSimpleNumber,
   isSimpleTemplateLiteral,
   isStringLiteral,
   isStringPropSafeToUnquote,