diff --git a/grammars/javascript.cson b/grammars/javascript.cson
index 09b456cb..51a88018 100644
--- a/grammars/javascript.cson
+++ b/grammars/javascript.cson
@@ -1245,45 +1245,70 @@
   'numbers':
     'patterns': [
       {
-        'match': '\\b(?<!\\$)0(x|X)[0-9a-fA-F]+n?\\b(?!\\$)'
+        'match': '\\b(?<!\\$)0(x|X)[0-9a-fA-F]+(?:_[0-9a-fA-F]+)*n?\\b(?!\\$)'
         'name': 'constant.numeric.hex.js'
+        'captures':
+          '0':
+            'patterns': [
+              {
+                'include': '#numeric_separators'
+              }
+            ]
       }
       {
-        'match': '\\b(?<!\\$)0(b|B)[01]+n?\\b(?!\\$)'
+        'match': '\\b(?<!\\$)0(b|B)[01]+(?:_[01]+)*n?\\b(?!\\$)'
         'name': 'constant.numeric.binary.js'
+        'captures':
+          '0':
+            'patterns': [
+              {
+                'include': '#numeric_separators'
+              }
+            ]
       }
       {
-        'match': '\\b(?<!\\$)0(o|O)?[0-7]+n?\\b(?!\\$)'
+        'match': '\\b(?<!\\$)0(o|O)?[0-7]+(?:_[0-7]+)*n?\\b(?!\\$)'
         'name': 'constant.numeric.octal.js'
+        'captures':
+          '0':
+            'patterns': [
+              {
+                'include': '#numeric_separators'
+              }
+            ]
       }
       {
         'match': '''(?x)
           (?<!\\$)(?:
-            (?:\\b[0-9]+(\\.)[0-9]+[eE][+-]?[0-9]+\\b)| # 1.1E+3
-            (?:\\b[0-9]+(\\.)[eE][+-]?[0-9]+\\b)|       # 1.E+3
-            (?:\\B(\\.)[0-9]+[eE][+-]?[0-9]+\\b)|       # .1E+3
-            (?:\\b[0-9]+[eE][+-]?[0-9]+\\b)|            # 1E+3
-            (?:\\b[0-9]+(\\.)[0-9]+\\b)|                # 1.1
-            (?:\\b[0-9]+(\\.)\\B)|                      # 1.
-            (?:\\B(\\.)[0-9]+\\b)|                      # .1
-            (?:\\b[0-9]+n?\\b(?!\\.))                   # 1n
+            (?:\\b[0-9]+(?:_[0-9]+)*\\.[0-9]+(?:_[0-9]+)*[eE][+-]?[0-9]+(?:_[0-9]+)*\\b)|   # 1.1E+3
+            (?:\\b[0-9]+(?:_[0-9]+)*\\.[eE][+-]?[0-9]+(?:_[0-9]+)*\\b)|                     # 1.E+3
+            (?:\\B\\.[0-9]+(?:_[0-9]+)*[eE][+-]?[0-9]+(?:_[0-9]+)*\\b)|                     # .1E+3
+            (?:\\b[0-9]+(?:_[0-9]+)*[eE][+-]?[0-9]+(?:_[0-9]+)*\\b)|                        # 1E+3
+            (?:\\b[0-9]+(?:_[0-9]+)*\\.[0-9]+(?:_[0-9]+)*\\b)|                              # 1.1
+            (?:\\b[0-9]+(?:_[0-9]+)*\\.\\B)|                                                # 1.
+            (?:\\B\\.[0-9]+(?:_[0-9]+)*\\b)|                                                # .1
+            (?:\\b[0-9]+(?:_[0-9]+)*n?\\b(?!\\.))                                           # 1n
           )(?!\\$)
         '''
+        'name': 'constant.numeric.decimal.js'
         'captures':
           '0':
-            'name': 'constant.numeric.decimal.js'
+            'patterns': [
+              {
+                'include': '#numeric_separators'
+              }
+            ]
+      }
+    ]
+  'numeric_separators':
+    'patterns': [
+      {
+        'match': '(_)|(\\.)'
+        'captures':
           '1':
-            'name': 'meta.delimiter.decimal.period.js'
+            'name': 'meta.delimiter.numeric.separator.js'
           '2':
             'name': 'meta.delimiter.decimal.period.js'
-          '3':
-            'name': 'meta.delimiter.decimal.period.js'
-          '4':
-            'name': 'meta.delimiter.decimal.period.js'
-          '5':
-            'name': 'meta.delimiter.decimal.period.js'
-          '6':
-            'name': 'meta.delimiter.decimal.period.js'
       }
     ]
   'operators':
diff --git a/spec/javascript-spec.coffee b/spec/javascript-spec.coffee
index 6c91abe4..f752b24e 100644
--- a/spec/javascript-spec.coffee
+++ b/spec/javascript-spec.coffee
@@ -323,6 +323,11 @@ describe "JavaScript grammar", ->
       {tokens} = grammar.tokenizeLine('0X1D306n')
       expect(tokens[0]).toEqual value: '0X1D306n', scopes: ['source.js', 'constant.numeric.hex.js']
 
+      {tokens} = grammar.tokenizeLine('0X1D30_69A3')
+      expect(tokens[0]).toEqual value: '0X1D30', scopes: ['source.js', 'constant.numeric.hex.js']
+      expect(tokens[1]).toEqual value: '_', scopes: ['source.js', 'constant.numeric.hex.js', 'meta.delimiter.numeric.separator.js']
+      expect(tokens[2]).toEqual value: '69A3', scopes: ['source.js', 'constant.numeric.hex.js']
+
     it "tokenizes binary literals", ->
       {tokens} = grammar.tokenizeLine('0b011101110111010001100110')
       expect(tokens[0]).toEqual value: '0b011101110111010001100110', scopes: ['source.js', 'constant.numeric.binary.js']
@@ -336,6 +341,19 @@ describe "JavaScript grammar", ->
       {tokens} = grammar.tokenizeLine('0B011101110111010001100110n')
       expect(tokens[0]).toEqual value: '0B011101110111010001100110n', scopes: ['source.js', 'constant.numeric.binary.js']
 
+      {tokens} = grammar.tokenizeLine('0B0111_0111_0111_0100_0110_0110')
+      expect(tokens[0]).toEqual value: '0B0111', scopes: ['source.js', 'constant.numeric.binary.js']
+      expect(tokens[1]).toEqual value: '_', scopes: ['source.js', 'constant.numeric.binary.js', 'meta.delimiter.numeric.separator.js']
+      expect(tokens[2]).toEqual value: '0111', scopes: ['source.js', 'constant.numeric.binary.js']
+      expect(tokens[3]).toEqual value: '_', scopes: ['source.js', 'constant.numeric.binary.js', 'meta.delimiter.numeric.separator.js']
+      expect(tokens[4]).toEqual value: '0111', scopes: ['source.js', 'constant.numeric.binary.js']
+      expect(tokens[5]).toEqual value: '_', scopes: ['source.js', 'constant.numeric.binary.js', 'meta.delimiter.numeric.separator.js']
+      expect(tokens[6]).toEqual value: '0100', scopes: ['source.js', 'constant.numeric.binary.js']
+      expect(tokens[7]).toEqual value: '_', scopes: ['source.js', 'constant.numeric.binary.js', 'meta.delimiter.numeric.separator.js']
+      expect(tokens[8]).toEqual value: '0110', scopes: ['source.js', 'constant.numeric.binary.js']
+      expect(tokens[9]).toEqual value: '_', scopes: ['source.js', 'constant.numeric.binary.js', 'meta.delimiter.numeric.separator.js']
+      expect(tokens[10]).toEqual value: '0110', scopes: ['source.js', 'constant.numeric.binary.js']
+
     it "tokenizes octal literals", ->
       {tokens} = grammar.tokenizeLine('0o1411')
       expect(tokens[0]).toEqual value: '0o1411', scopes: ['source.js', 'constant.numeric.octal.js']
@@ -352,6 +370,18 @@ describe "JavaScript grammar", ->
       {tokens} = grammar.tokenizeLine('0010')
       expect(tokens[0]).toEqual value: '0010', scopes: ['source.js', 'constant.numeric.octal.js']
 
+      {tokens} = grammar.tokenizeLine('0010_7201_5112')
+      expect(tokens[0]).toEqual value: '0010', scopes: ['source.js', 'constant.numeric.octal.js']
+      expect(tokens[1]).toEqual value: '_', scopes: ['source.js', 'constant.numeric.octal.js', 'meta.delimiter.numeric.separator.js']
+      expect(tokens[2]).toEqual value: '7201', scopes: ['source.js', 'constant.numeric.octal.js']
+      expect(tokens[3]).toEqual value: '_', scopes: ['source.js', 'constant.numeric.octal.js', 'meta.delimiter.numeric.separator.js']
+      expect(tokens[4]).toEqual value: '5112', scopes: ['source.js', 'constant.numeric.octal.js']
+
+      {tokens} = grammar.tokenizeLine('0O1411_1236')
+      expect(tokens[0]).toEqual value: '0O1411', scopes: ['source.js', 'constant.numeric.octal.js']
+      expect(tokens[1]).toEqual value: '_', scopes: ['source.js', 'constant.numeric.octal.js', 'meta.delimiter.numeric.separator.js']
+      expect(tokens[2]).toEqual value: '1236', scopes: ['source.js', 'constant.numeric.octal.js']
+
     it "tokenizes decimals", ->
       {tokens} = grammar.tokenizeLine('1234')
       expect(tokens[0]).toEqual value: '1234', scopes: ['source.js', 'constant.numeric.decimal.js']
@@ -359,6 +389,13 @@ describe "JavaScript grammar", ->
       {tokens} = grammar.tokenizeLine('123456789n')
       expect(tokens[0]).toEqual value: '123456789n', scopes: ['source.js', 'constant.numeric.decimal.js']
 
+      {tokens} = grammar.tokenizeLine('123_456_789n')
+      expect(tokens[0]).toEqual value: '123', scopes: ['source.js', 'constant.numeric.decimal.js']
+      expect(tokens[1]).toEqual value: '_', scopes: ['source.js', 'constant.numeric.decimal.js', 'meta.delimiter.numeric.separator.js']
+      expect(tokens[2]).toEqual value: '456', scopes: ['source.js', 'constant.numeric.decimal.js']
+      expect(tokens[3]).toEqual value: '_', scopes: ['source.js', 'constant.numeric.decimal.js', 'meta.delimiter.numeric.separator.js']
+      expect(tokens[4]).toEqual value: '789n', scopes: ['source.js', 'constant.numeric.decimal.js']
+
       {tokens} = grammar.tokenizeLine('5e-10')
       expect(tokens[0]).toEqual value: '5e-10', scopes: ['source.js', 'constant.numeric.decimal.js']
 
@@ -369,24 +406,92 @@ describe "JavaScript grammar", ->
       expect(tokens[0]).toEqual value: '9', scopes: ['source.js', 'constant.numeric.decimal.js']
       expect(tokens[1]).toEqual value: '.', scopes: ['source.js', 'constant.numeric.decimal.js', 'meta.delimiter.decimal.period.js']
 
+      {tokens} = grammar.tokenizeLine('9_9.')
+      expect(tokens[0]).toEqual value: '9', scopes: ['source.js', 'constant.numeric.decimal.js']
+      expect(tokens[1]).toEqual value: '_', scopes: ['source.js', 'constant.numeric.decimal.js', 'meta.delimiter.numeric.separator.js']
+      expect(tokens[2]).toEqual value: '9', scopes: ['source.js', 'constant.numeric.decimal.js']
+      expect(tokens[3]).toEqual value: '.', scopes: ['source.js', 'constant.numeric.decimal.js', 'meta.delimiter.decimal.period.js']
+
       {tokens} = grammar.tokenizeLine('.9')
       expect(tokens[0]).toEqual value: '.', scopes: ['source.js', 'constant.numeric.decimal.js', 'meta.delimiter.decimal.period.js']
       expect(tokens[1]).toEqual value: '9', scopes: ['source.js', 'constant.numeric.decimal.js']
 
+      {tokens} = grammar.tokenizeLine('.9_9')
+      expect(tokens[0]).toEqual value: '.', scopes: ['source.js', 'constant.numeric.decimal.js', 'meta.delimiter.decimal.period.js']
+      expect(tokens[1]).toEqual value: '9', scopes: ['source.js', 'constant.numeric.decimal.js']
+      expect(tokens[2]).toEqual value: '_', scopes: ['source.js', 'constant.numeric.decimal.js', 'meta.delimiter.numeric.separator.js']
+      expect(tokens[3]).toEqual value: '9', scopes: ['source.js', 'constant.numeric.decimal.js']
+
       {tokens} = grammar.tokenizeLine('9.9')
       expect(tokens[0]).toEqual value: '9', scopes: ['source.js', 'constant.numeric.decimal.js']
       expect(tokens[1]).toEqual value: '.', scopes: ['source.js', 'constant.numeric.decimal.js', 'meta.delimiter.decimal.period.js']
       expect(tokens[2]).toEqual value: '9', scopes: ['source.js', 'constant.numeric.decimal.js']
 
+      {tokens} = grammar.tokenizeLine('9_9.9_9')
+      expect(tokens[0]).toEqual value: '9', scopes: ['source.js', 'constant.numeric.decimal.js']
+      expect(tokens[1]).toEqual value: '_', scopes: ['source.js', 'constant.numeric.decimal.js', 'meta.delimiter.numeric.separator.js']
+      expect(tokens[2]).toEqual value: '9', scopes: ['source.js', 'constant.numeric.decimal.js']
+      expect(tokens[3]).toEqual value: '.', scopes: ['source.js', 'constant.numeric.decimal.js', 'meta.delimiter.decimal.period.js']
+      expect(tokens[4]).toEqual value: '9', scopes: ['source.js', 'constant.numeric.decimal.js']
+      expect(tokens[5]).toEqual value: '_', scopes: ['source.js', 'constant.numeric.decimal.js', 'meta.delimiter.numeric.separator.js']
+      expect(tokens[6]).toEqual value: '9', scopes: ['source.js', 'constant.numeric.decimal.js']
+
       {tokens} = grammar.tokenizeLine('.1e-23')
       expect(tokens[0]).toEqual value: '.', scopes: ['source.js', 'constant.numeric.decimal.js', 'meta.delimiter.decimal.period.js']
       expect(tokens[1]).toEqual value: '1e-23', scopes: ['source.js', 'constant.numeric.decimal.js']
 
+      {tokens} = grammar.tokenizeLine('.1_1E+1_1')
+      expect(tokens[0]).toEqual value: '.', scopes: ['source.js', 'constant.numeric.decimal.js', 'meta.delimiter.decimal.period.js']
+      expect(tokens[1]).toEqual value: '1', scopes: ['source.js', 'constant.numeric.decimal.js']
+      expect(tokens[2]).toEqual value: '_', scopes: ['source.js', 'constant.numeric.decimal.js', 'meta.delimiter.numeric.separator.js']
+      expect(tokens[3]).toEqual value: '1E+1', scopes: ['source.js', 'constant.numeric.decimal.js']
+      expect(tokens[4]).toEqual value: '_', scopes: ['source.js', 'constant.numeric.decimal.js', 'meta.delimiter.numeric.separator.js']
+      expect(tokens[5]).toEqual value: '1', scopes: ['source.js', 'constant.numeric.decimal.js']
+
       {tokens} = grammar.tokenizeLine('1.E3')
       expect(tokens[0]).toEqual value: '1', scopes: ['source.js', 'constant.numeric.decimal.js']
       expect(tokens[1]).toEqual value: '.', scopes: ['source.js', 'constant.numeric.decimal.js', 'meta.delimiter.decimal.period.js']
       expect(tokens[2]).toEqual value: 'E3', scopes: ['source.js', 'constant.numeric.decimal.js']
 
+      {tokens} = grammar.tokenizeLine('1_1.E-1_1')
+      expect(tokens[0]).toEqual value: '1', scopes: ['source.js', 'constant.numeric.decimal.js']
+      expect(tokens[1]).toEqual value: '_', scopes: ['source.js', 'constant.numeric.decimal.js', 'meta.delimiter.numeric.separator.js']
+      expect(tokens[2]).toEqual value: '1', scopes: ['source.js', 'constant.numeric.decimal.js']
+      expect(tokens[3]).toEqual value: '.', scopes: ['source.js', 'constant.numeric.decimal.js', 'meta.delimiter.decimal.period.js']
+      expect(tokens[4]).toEqual value: 'E-1', scopes: ['source.js', 'constant.numeric.decimal.js']
+      expect(tokens[5]).toEqual value: '_', scopes: ['source.js', 'constant.numeric.decimal.js', 'meta.delimiter.numeric.separator.js']
+      expect(tokens[6]).toEqual value: '1', scopes: ['source.js', 'constant.numeric.decimal.js']
+
+      {tokens} = grammar.tokenizeLine('1_1.1_1E1_1')
+      expect(tokens[0]).toEqual value: '1', scopes: ['source.js', 'constant.numeric.decimal.js']
+      expect(tokens[1]).toEqual value: '_', scopes: ['source.js', 'constant.numeric.decimal.js', 'meta.delimiter.numeric.separator.js']
+      expect(tokens[2]).toEqual value: '1', scopes: ['source.js', 'constant.numeric.decimal.js']
+      expect(tokens[3]).toEqual value: '.', scopes: ['source.js', 'constant.numeric.decimal.js', 'meta.delimiter.decimal.period.js']
+      expect(tokens[4]).toEqual value: '1', scopes: ['source.js', 'constant.numeric.decimal.js']
+      expect(tokens[5]).toEqual value: '_', scopes: ['source.js', 'constant.numeric.decimal.js', 'meta.delimiter.numeric.separator.js']
+      expect(tokens[6]).toEqual value: '1E1', scopes: ['source.js', 'constant.numeric.decimal.js']
+      expect(tokens[7]).toEqual value: '_', scopes: ['source.js', 'constant.numeric.decimal.js', 'meta.delimiter.numeric.separator.js']
+      expect(tokens[8]).toEqual value: '1', scopes: ['source.js', 'constant.numeric.decimal.js']
+
+      {tokens} = grammar.tokenizeLine('9_9')
+      expect(tokens[0]).toEqual value: '9', scopes: ['source.js', 'constant.numeric.decimal.js']
+      expect(tokens[1]).toEqual value: '_', scopes: ['source.js', 'constant.numeric.decimal.js', 'meta.delimiter.numeric.separator.js']
+      expect(tokens[2]).toEqual value: '9', scopes: ['source.js', 'constant.numeric.decimal.js']
+
+      {tokens} = grammar.tokenizeLine('9_9_9')
+      expect(tokens[0]).toEqual value: '9', scopes: ['source.js', 'constant.numeric.decimal.js']
+      expect(tokens[1]).toEqual value: '_', scopes: ['source.js', 'constant.numeric.decimal.js', 'meta.delimiter.numeric.separator.js']
+      expect(tokens[2]).toEqual value: '9', scopes: ['source.js', 'constant.numeric.decimal.js']
+      expect(tokens[3]).toEqual value: '_', scopes: ['source.js', 'constant.numeric.decimal.js', 'meta.delimiter.numeric.separator.js']
+      expect(tokens[4]).toEqual value: '9', scopes: ['source.js', 'constant.numeric.decimal.js']
+
+      {tokens} = grammar.tokenizeLine('999_999_999')
+      expect(tokens[0]).toEqual value: '999', scopes: ['source.js', 'constant.numeric.decimal.js']
+      expect(tokens[1]).toEqual value: '_', scopes: ['source.js', 'constant.numeric.decimal.js', 'meta.delimiter.numeric.separator.js']
+      expect(tokens[2]).toEqual value: '999', scopes: ['source.js', 'constant.numeric.decimal.js']
+      expect(tokens[3]).toEqual value: '_', scopes: ['source.js', 'constant.numeric.decimal.js', 'meta.delimiter.numeric.separator.js']
+      expect(tokens[4]).toEqual value: '999', scopes: ['source.js', 'constant.numeric.decimal.js']
+
     it "does not tokenize numbers that are part of a variable", ->
       {tokens} = grammar.tokenizeLine('hi$1')
       expect(tokens[0]).toEqual value: 'hi$1', scopes: ['source.js']
@@ -394,6 +499,17 @@ describe "JavaScript grammar", ->
       {tokens} = grammar.tokenizeLine('hi_1')
       expect(tokens[0]).toEqual value: 'hi_1', scopes: ['source.js']
 
+      {tokens} = grammar.tokenizeLine('_1')
+      expect(tokens[0]).toEqual value: '_1', scopes: ['source.js', 'constant.other.js']
+
+      {tokens} = grammar.tokenizeLine('1_')
+      expect(tokens[0]).toEqual value: '1_', scopes: ['source.js', 'invalid.illegal.identifier.js']
+
+      {tokens} = grammar.tokenizeLine('1_._1')
+      expect(tokens[0]).toEqual value: '1_', scopes: ['source.js', 'invalid.illegal.identifier.js']
+      expect(tokens[1]).toEqual value: '.', scopes: ['source.js', 'meta.delimiter.property.period.js']
+      expect(tokens[2]).toEqual value: '_1', scopes: ['source.js', 'variable.other.property.js']
+
   describe "operators", ->
     it "tokenizes them", ->
       operators = ["delete", "in", "of", "instanceof", "new", "typeof", "void"]