[New] add numericSeparator boolean option

node v17.3.0 adds this

index.js

@@ -16,7 +16,10 @@ var booleanValueOf = Boolean.prototype.valueOf;
 var objectToString = Object.prototype.toString;
 var functionToString = Function.prototype.toString;
 var match = String.prototype.match;
+var $slice = String.prototype.slice;
+var $replace = String.prototype.replace;
 var test = RegExp.prototype.test;
+var $floor = Math.floor;
 var bigIntValueOf = typeof BigInt === 'function' ? BigInt.prototype.valueOf : null;
 var gOPS = Object.getOwnPropertySymbols;
 var symToString = typeof Symbol === 'function' && typeof Symbol.iterator === 'symbol' ? Symbol.prototype.toString : null;
@@ -35,6 +38,28 @@ var gPO = (typeof Reflect === 'function' ? Reflect.getPrototypeOf : Object.getPr
         : null
 );
 
+function addNumericSeparator(num, str) {
+    if (
+        num === Infinity
+        || num === -Infinity
+        || num !== num
+        || (num && num > -1000 && num < 1000)
+        || test.call(/e/, str)
+    ) {
+        return str;
+    }
+    var sepRegex = /[0-9](?=(?:[0-9]{3})+(?![0-9]))/g;
+    if (typeof num === 'number') {
+        var int = num < 0 ? -$floor(-num) : $floor(num); // trunc(num)
+        if (int !== num) {
+            var intStr = String(int);
+            var dec = $slice.call(str, intStr.length + 1);
+            return $replace.call(intStr, sepRegex, '$&_') + '.' + $replace.call($replace.call(dec, /([0-9]{3})/g, '$&_'), /_$/, '');
+        }
+    }
+    return $replace.call(str, sepRegex, '$&_');
+}
+
 var inspectCustom = require('./util.inspect').custom;
 var inspectSymbol = inspectCustom && isSymbol(inspectCustom) ? inspectCustom : null;
 
@@ -63,8 +88,12 @@ module.exports = function inspect_(obj, options, depth, seen) {
         && opts.indent !== '\t'
         && !(parseInt(opts.indent, 10) === opts.indent && opts.indent > 0)
     ) {
-        throw new TypeError('options "indent" must be "\\t", an integer > 0, or `null`');
+        throw new TypeError('option "indent" must be "\\t", an integer > 0, or `null`');
+    }
+    if (has(opts, 'numericSeparator') && typeof opts.numericSeparator !== 'boolean') {
+        throw new TypeError('option "numericSeparator", if provided, must be `true` or `false`');
     }
+    var numericSeparator = opts.numericSeparator;
 
     if (typeof obj === 'undefined') {
         return 'undefined';
@@ -83,10 +112,12 @@ module.exports = function inspect_(obj, options, depth, seen) {
         if (obj === 0) {
             return Infinity / obj > 0 ? '0' : '-0';
         }
-        return String(obj);
+        var str = String(obj);
+        return numericSeparator ? addNumericSeparator(obj, str) : str;
     }
     if (typeof obj === 'bigint') {
-        return String(obj) + 'n';
+        var bigIntStr = String(obj) + 'n';
+        return numericSeparator ? addNumericSeparator(obj, bigIntStr) : bigIntStr;
     }
 
     var maxDepth = typeof opts.depth === 'undefined' ? 5 : opts.depth;

package.json

@@ -9,6 +9,7 @@
     "aud": "^1.1.5",
     "auto-changelog": "^2.3.0",
     "core-js": "^2.6.12",
+    "es-value-fixtures": "^1.2.1",
     "eslint": "^8.4.0",
     "for-each": "^0.3.3",
     "functions-have-names": "^1.2.2",

readme.markdown

@@ -55,6 +55,7 @@ Additional options:
   - `maxStringLength`: must be `0`, a positive integer, `Infinity`, or `null`, if present. Default `Infinity`.
   - `customInspect`: When `true`, a custom inspect method function will be invoked (either undere the `util.inspect.custom` symbol, or the `inspect` property). When the string `'symbol'`, only the symbol method will be invoked. Default `true`.
   - `indent`: must be "\t", `null`, or a positive integer. Default `null`.
+  - `numericSeparator`: must be a boolean, if present. Default `false`. If `true`, all numbers will be printed with numeric separators (eg, `1234.5678` will be printed as `'1_234.567_8'`)
 
 # install
 

test/bigint.js

@@ -42,5 +42,17 @@ test('bigint', { skip: typeof BigInt === 'undefined' }, function (t) {
         );
     });
 
+    t.test('numericSeparator', function (st) {
+        st.equal(inspect(BigInt(0), { numericSeparator: false }), '0n', '0n, numericSeparator false');
+        st.equal(inspect(BigInt(0), { numericSeparator: true }), '0n', '0n, numericSeparator true');
+
+        st.equal(inspect(BigInt(1234), { numericSeparator: false }), '1234n', '1234n, numericSeparator false');
+        st.equal(inspect(BigInt(1234), { numericSeparator: true }), '1_234n', '1234n, numericSeparator true');
+        st.equal(inspect(BigInt(-1234), { numericSeparator: false }), '-1234n', '1234n, numericSeparator false');
+        st.equal(inspect(BigInt(-1234), { numericSeparator: true }), '-1_234n', '1234n, numericSeparator true');
+
+        st.end();
+    });
+
     t.end();
 });

test/number.js

@@ -1,5 +1,8 @@
-var inspect = require('../');
 var test = require('tape');
+var v = require('es-value-fixtures');
+var forEach = require('for-each');
+
+var inspect = require('../');
 
 test('negative zero', function (t) {
     t.equal(inspect(0), '0', 'inspect(0) === "0"');
@@ -10,3 +13,46 @@ test('negative zero', function (t) {
 
     t.end();
 });
+
+test('numericSeparator', function (t) {
+    forEach(v.nonBooleans, function (nonBoolean) {
+        t['throws'](
+            function () { inspect(true, { numericSeparator: nonBoolean }); },
+            TypeError,
+            inspect(nonBoolean) + ' is not a boolean'
+        );
+    });
+
+    t.test('3 digit numbers', function (st) {
+        var failed = false;
+        for (var i = -999; i < 1000; i += 1) {
+            var actual = inspect(i);
+            var actualSepNo = inspect(i, { numericSeparator: false });
+            var actualSepYes = inspect(i, { numericSeparator: true });
+            var expected = String(i);
+            if (actual !== expected || actualSepNo !== expected || actualSepYes !== expected) {
+                failed = true;
+                t.equal(actual, expected);
+                t.equal(actualSepNo, expected);
+                t.equal(actualSepYes, expected);
+            }
+        }
+
+        st.notOk(failed, 'all 3 digit numbers passed');
+
+        st.end();
+    });
+
+    t.equal(inspect(1e3), '1000', '1000');
+    t.equal(inspect(1e3, { numericSeparator: false }), '1000', '1000, numericSeparator false');
+    t.equal(inspect(1e3, { numericSeparator: true }), '1_000', '1000, numericSeparator true');
+    t.equal(inspect(-1e3), '-1000', '-1000');
+    t.equal(inspect(-1e3, { numericSeparator: false }), '-1000', '-1000, numericSeparator false');
+    t.equal(inspect(-1e3, { numericSeparator: true }), '-1_000', '-1000, numericSeparator true');
+
+    t.equal(inspect(1234.5678, { numericSeparator: true }), '1_234.567_8', 'fractional numbers get separators');
+    t.equal(inspect(1234.56789, { numericSeparator: true }), '1_234.567_89', 'fractional numbers get separators');
+    t.equal(inspect(1234.567891, { numericSeparator: true }), '1_234.567_891', 'fractional numbers get separators');
+
+    t.end();
+});