util: add numericSeparator to util.inspect

This adds the `numericSeparator` option to util.inspect. Using it
separates numbers by thousands adding the underscore accordingly.

Signed-off-by: Ruben Bridgewater <ruben@bridgewater.de>

PR-URL: https://github.com/nodejs/node/pull/41003
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>

1 files changed, 21 insertions, 0 deletions

diff --git a/doc/api/util.md b/doc/api/util.md
index 3810b1145cd..3b4078b6dc8 100644
--- a/doc/api/util.md
+++ b/doc/api/util.md
@@ -485,6 +485,9 @@ stream.write('With ES6');
 <!-- YAML
 added: v0.3.0
 changes:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/41003
+    description: The `numericSeparator` option is supported now.
   - version:
     - v14.6.0
     - v12.19.0
@@ -606,6 +609,9 @@ changes:
     set to `'set'`, only getters with a corresponding setter are inspected.
     This might cause side effects depending on the getter function.
     **Default:** `false`.
+  * `numericSeparator` {boolean} If set to `true`, an underscore is used to
+    separate every three digits in all bigints and numbers.
+    **Default:** `false`.
 * Returns: {string} The representation of `object`.
 
 The `util.inspect()` method returns a string representation of `object` that is
@@ -754,6 +760,21 @@ assert.strict.equal(
 );
 ```
 
+The `numericSeparator` option adds an underscore every three digits to all
+numbers.
+
+```js
+const { inspect } = require('util');
+
+const thousand = 1_000;
+const million = 1_000_000;
+const bigNumber = 123_456_789n;
+const bigDecimal = 1_234.123_45;
+
+console.log(thousand, million, bigNumber, bigDecimal);
+// 1_000 1_000_000 123_456_789n 1_234.123_45
+```
+
 `util.inspect()` is a synchronous method intended for debugging. Its maximum
 output length is approximately 128 MB. Inputs that result in longer output will
 be truncated.