diff --git a/Documentation/gitattributes.txt b/Documentation/gitattributes.txt
index 60984a4682..a8e3e4d735 100644
--- a/Documentation/gitattributes.txt
+++ b/Documentation/gitattributes.txt
@@ -828,6 +828,8 @@ patterns are available:
 
 - `java` suitable for source code in the Java language.
 
+- `javascript` suitable for source code in the JavaScript language.
+
 - `markdown` suitable for Markdown documents.
 
 - `matlab` suitable for source code in the MATLAB and Octave languages.
diff --git a/t/t4018/javascript-assignment-of-anonymous-function b/t/t4018/javascript-assignment-of-anonymous-function
new file mode 100644
index 0000000000..b6f2ccccfc
--- /dev/null
+++ b/t/t4018/javascript-assignment-of-anonymous-function
@@ -0,0 +1,4 @@
+const RIGHT = function (a, b) {
+	
+    return a + b; // ChangeMe
+};
diff --git a/t/t4018/javascript-assignment-of-arrow-function b/t/t4018/javascript-assignment-of-arrow-function
new file mode 100644
index 0000000000..24ce517b7a
--- /dev/null
+++ b/t/t4018/javascript-assignment-of-arrow-function
@@ -0,0 +1,4 @@
+const RIGHT = (a, b) => {
+	
+    return a + b; // ChangeMe
+};
diff --git a/t/t4018/javascript-assignment-of-arrow-function-2 b/t/t4018/javascript-assignment-of-arrow-function-2
new file mode 100644
index 0000000000..bbf5de369e
--- /dev/null
+++ b/t/t4018/javascript-assignment-of-arrow-function-2
@@ -0,0 +1,4 @@
+const RIGHT = (a, b)=>{
+	
+    return a + b; // ChangeMe
+};
diff --git a/t/t4018/javascript-assignment-of-arrow-function-3 b/t/t4018/javascript-assignment-of-arrow-function-3
new file mode 100644
index 0000000000..4a07aa3259
--- /dev/null
+++ b/t/t4018/javascript-assignment-of-arrow-function-3
@@ -0,0 +1,4 @@
+const RIGHT=test=>{
+	
+    return test + 1; // ChangeMe
+};
diff --git a/t/t4018/javascript-assignment-of-named-function b/t/t4018/javascript-assignment-of-named-function
new file mode 100644
index 0000000000..bfc486ebef
--- /dev/null
+++ b/t/t4018/javascript-assignment-of-named-function
@@ -0,0 +1,4 @@
+const RIGHT = function test (a, b) {
+	
+    return a + b; // ChangeMe
+};
diff --git a/t/t4018/javascript-async-function b/t/t4018/javascript-async-function
new file mode 100644
index 0000000000..993e6926bf
--- /dev/null
+++ b/t/t4018/javascript-async-function
@@ -0,0 +1,4 @@
+async function RIGHT(a, b) {
+  
+  return a + b; // ChangeMe
+}
diff --git a/t/t4018/javascript-es5-method-shorthand b/t/t4018/javascript-es5-method-shorthand
new file mode 100644
index 0000000000..01fc0cc34b
--- /dev/null
+++ b/t/t4018/javascript-es5-method-shorthand
@@ -0,0 +1,6 @@
+const foo = {
+    RIGHT() {
+        
+        console.log('ChangeMe');
+    }
+}
diff --git a/t/t4018/javascript-export-async-function b/t/t4018/javascript-export-async-function
new file mode 100644
index 0000000000..fecbd669d7
--- /dev/null
+++ b/t/t4018/javascript-export-async-function
@@ -0,0 +1,4 @@
+export async function RIGHT(a, b) {
+  
+  return a + b; // ChangeMe
+}
diff --git a/t/t4018/javascript-export-function b/t/t4018/javascript-export-function
new file mode 100644
index 0000000000..b5acbb2b08
--- /dev/null
+++ b/t/t4018/javascript-export-function
@@ -0,0 +1,4 @@
+export function RIGHT(a, b) {
+  
+  return a + b; // ChangeMe
+}
diff --git a/t/t4018/javascript-exports-anomyous-function b/t/t4018/javascript-exports-anomyous-function
new file mode 100644
index 0000000000..6786cbda8d
--- /dev/null
+++ b/t/t4018/javascript-exports-anomyous-function
@@ -0,0 +1,4 @@
+exports.setFlagged = RIGHT => {
+	
+    return ChangeMe;
+};
diff --git a/t/t4018/javascript-exports-anomyous-function-2 b/t/t4018/javascript-exports-anomyous-function-2
new file mode 100644
index 0000000000..883569f40d
--- /dev/null
+++ b/t/t4018/javascript-exports-anomyous-function-2
@@ -0,0 +1,4 @@
+exports.RIGHT = (a, b, runtime) => {
+	
+    return ChangeMe;
+};
diff --git a/t/t4018/javascript-exports-anomyous-function-3 b/t/t4018/javascript-exports-anomyous-function-3
new file mode 100644
index 0000000000..bc78ed87eb
--- /dev/null
+++ b/t/t4018/javascript-exports-anomyous-function-3
@@ -0,0 +1,4 @@
+module.exports.RIGHT = (a, b, runtime) => {
+	
+    return ChangeMe;
+};
diff --git a/t/t4018/javascript-exports-anomyous-function-4 b/t/t4018/javascript-exports-anomyous-function-4
new file mode 100644
index 0000000000..b952cf2a5a
--- /dev/null
+++ b/t/t4018/javascript-exports-anomyous-function-4
@@ -0,0 +1,4 @@
+module.exports = ( RIGHT ) => {
+	
+    return ChangeMe;
+};
diff --git a/t/t4018/javascript-exports-function b/t/t4018/javascript-exports-function
new file mode 100644
index 0000000000..63b79f5991
--- /dev/null
+++ b/t/t4018/javascript-exports-function
@@ -0,0 +1,4 @@
+exports.RIGHT = function(document) {
+    
+    return ChangeMe;
+}
diff --git a/t/t4018/javascript-function b/t/t4018/javascript-function
new file mode 100644
index 0000000000..0cc0bf54e7
--- /dev/null
+++ b/t/t4018/javascript-function
@@ -0,0 +1,4 @@
+function RIGHT(a, b) {
+
+  return a + b; // ChangeMe
+}
diff --git a/t/t4018/javascript-function-in-class b/t/t4018/javascript-function-in-class
new file mode 100644
index 0000000000..0cc0a26612
--- /dev/null
+++ b/t/t4018/javascript-function-in-class
@@ -0,0 +1,6 @@
+class Test {
+  RIGHT() {
+    let a = 4;
+    let b = ChangeMe;
+  }
+}
diff --git a/t/t4018/javascript-function-in-class-2 b/t/t4018/javascript-function-in-class-2
new file mode 100644
index 0000000000..725495fe55
--- /dev/null
+++ b/t/t4018/javascript-function-in-class-2
@@ -0,0 +1,11 @@
+class Test {
+  RIGHT(
+      aaaaaaaaaa,
+      bbbbbbbbbb,
+      cccccccccc,
+      dddddddddd
+  ) {
+    let a = 4;
+    let b = ChangeMe;
+  }
+}
diff --git a/t/t4018/javascript-function-in-class-3 b/t/t4018/javascript-function-in-class-3
new file mode 100644
index 0000000000..e9b20728b2
--- /dev/null
+++ b/t/t4018/javascript-function-in-class-3
@@ -0,0 +1,10 @@
+class Test {
+  RIGHT(aaaaaaaaaa,
+      bbbbbbbbbb,
+      cccccccccc,
+      dddddddddd
+  ) {
+    let a = 4;
+    let b = ChangeMe;
+  }
+}
diff --git a/t/t4018/javascript-function-in-object-literal b/t/t4018/javascript-function-in-object-literal
new file mode 100644
index 0000000000..021cc706dd
--- /dev/null
+++ b/t/t4018/javascript-function-in-object-literal
@@ -0,0 +1,7 @@
+const obj = {
+    RIGHT: function (elems, callback, arg) {
+        var length, value;
+        // ...
+        return ChangeMe
+    }
+}
diff --git a/t/t4018/javascript-generator-function b/t/t4018/javascript-generator-function
new file mode 100644
index 0000000000..dc7793939f
--- /dev/null
+++ b/t/t4018/javascript-generator-function
@@ -0,0 +1,4 @@
+function* RIGHT(a, b) {
+  
+  return a + b; // ChangeMe
+}
diff --git a/t/t4018/javascript-generator-function-2 b/t/t4018/javascript-generator-function-2
new file mode 100644
index 0000000000..950676a612
--- /dev/null
+++ b/t/t4018/javascript-generator-function-2
@@ -0,0 +1,4 @@
+function *RIGHT(a, b) {
+  
+  return a + b; // ChangeMe
+}
diff --git a/t/t4018/javascript-getter-function-in-class b/t/t4018/javascript-getter-function-in-class
new file mode 100644
index 0000000000..9a5aee39f7
--- /dev/null
+++ b/t/t4018/javascript-getter-function-in-class
@@ -0,0 +1,6 @@
+class Test {
+  get RIGHT() {
+    let a = 4;
+    let b = ChangeMe;
+  }
+}
diff --git a/t/t4018/javascript-setter-function-in-class b/t/t4018/javascript-setter-function-in-class
new file mode 100644
index 0000000000..dc5f288665
--- /dev/null
+++ b/t/t4018/javascript-setter-function-in-class
@@ -0,0 +1,6 @@
+class Test {
+  set RIGHT() {
+    let a = 4;
+    let b = ChangeMe;
+  }
+}
diff --git a/t/t4018/javascript-skip-chained-function b/t/t4018/javascript-skip-chained-function
new file mode 100644
index 0000000000..4ce23901cf
--- /dev/null
+++ b/t/t4018/javascript-skip-chained-function
@@ -0,0 +1,5 @@
+function RIGHT(a, b) {
+
+  expect(spy.calls.count()).toBe(1)
+  return a + b; // ChangeMe
+}
diff --git a/t/t4018/javascript-skip-function-call-statement b/t/t4018/javascript-skip-function-call-statement
new file mode 100644
index 0000000000..321993c27e
--- /dev/null
+++ b/t/t4018/javascript-skip-function-call-statement
@@ -0,0 +1,7 @@
+class Test {
+  static RIGHT() {
+    haha();
+    haha2()
+    let b = ChangeMe;
+  }
+}
diff --git a/t/t4018/javascript-skip-keywords b/t/t4018/javascript-skip-keywords
new file mode 100644
index 0000000000..5584970b58
--- /dev/null
+++ b/t/t4018/javascript-skip-keywords
@@ -0,0 +1,34 @@
+function RIGHT(a, b) {
+  import("./async1")
+  if (a > 1) {
+    // ...
+  }
+  do {
+    // ...
+  } while (i < 5);
+  for (const element of array1) {
+    console.log(element)
+  }
+  with(o) {
+    console.log(x)
+  }
+  switch (expr) {
+    case 'a':
+      // ...
+      break;
+    case 'b':
+      // ...
+      break;
+    default:
+      // ...
+  }
+  try {
+    // ...
+    return (a + c)
+  } 
+  catch (error) {
+    // ...
+  }
+
+  return a + b; // ChangeMe
+}
diff --git a/t/t4018/javascript-static-function-in-class b/t/t4018/javascript-static-function-in-class
new file mode 100644
index 0000000000..fbf0b7ca3d
--- /dev/null
+++ b/t/t4018/javascript-static-function-in-class
@@ -0,0 +1,6 @@
+class Test {
+  static RIGHT() {
+    let a = 4;
+    let b = ChangeMe;
+  }
+}
diff --git a/t/t4034-diff-words.sh b/t/t4034-diff-words.sh
index d5abcf4b4c..33073edeca 100755
--- a/t/t4034-diff-words.sh
+++ b/t/t4034-diff-words.sh
@@ -324,6 +324,7 @@ test_language_driver dts
 test_language_driver fortran
 test_language_driver html
 test_language_driver java
+test_language_driver javascript
 test_language_driver matlab
 test_language_driver objc
 test_language_driver pascal
diff --git a/t/t4034/javascript/expect b/t/t4034/javascript/expect
new file mode 100644
index 0000000000..419d61903b
--- /dev/null
+++ b/t/t4034/javascript/expect
@@ -0,0 +1,54 @@
+<BOLD>diff --git a/pre b/post<RESET>
+<BOLD>index 18f4796..46f9b62 100644<RESET>
+<BOLD>--- a/pre<RESET>
+<BOLD>+++ b/post<RESET>
+<CYAN>@@ -1,33 +1,33 @@<RESET>
+// DecimalLiteral<RESET>
+<RED>123<RESET>
+<RED>0.123<RESET>
+<RED>.123<RESET>
+<RED>0.123e+5<RESET>
+<RED>0.123E+5<RESET>
+<RED>0.123e5<RESET>
+<RED>1222222222222222223334444n<RESET><GREEN>124<RESET>
+<GREEN>0.124<RESET>
+<GREEN>.124<RESET>
+<GREEN>0.123e-5<RESET>
+<GREEN>0.123E-5<RESET>
+<GREEN>0.123E5<RESET>
+<GREEN>12222222222222222233344445n<RESET>
+// HexIntegerLiteral<RESET>
+<RED>0x10<RESET>
+<RED>0X6Fa1<RESET>
+<RED>0x123_456<RESET>
+<RED>0x1234182989812f1289an<RESET><GREEN>0x11<RESET>
+<GREEN>0X5Fa1<RESET>
+<GREEN>0x123_756<RESET>
+<GREEN>0x1234182989812f1289bn<RESET>
+// OctalIntegerLiteral<RESET>
+<RED>05<RESET>
+<RED>0o6<RESET>
+<RED>0O7<RESET>
+<RED>0512_567<RESET>
+<RED>0o424242424242424242424242424242666666n<RESET><GREEN>06<RESET>
+<GREEN>0o5<RESET>
+<GREEN>0O4<RESET>
+<GREEN>0511_567<RESET>
+<GREEN>0o424242424242424242424242424242666667n<RESET>
+// BinaryIntegerLiteral<RESET>
+<RED>0b1001<RESET>
+<RED>0B0110<RESET>
+<RED>0b0001_1001_0011<RESET>
+<RED>0b1111111111111111111111111111111111111n<RESET><GREEN>0b1101<RESET>
+<GREEN>0B0010<RESET>
+<GREEN>0b0001_1101_0011<RESET>
+<GREEN>0b11111111111111000011111111111111111n<RESET>
+// punctuations<RESET>
+{<RED>a<RESET><GREEN>b<RESET>} (<RED>a<RESET><GREEN>b<RESET>)
+<RED>a<RESET><GREEN>b<RESET>;
+[<RED>1,<RESET>2<GREEN>,3<RESET>]
+[<RED>1, 2,<RESET> ...<RED>params<RESET><GREEN>params_v2<RESET> ]
+a<RED><=<RESET><GREEN>=<RESET>2 a<RED>>=<RESET><GREEN>=<RESET>2 a<RED>==<RESET><GREEN>=<RESET>2 a<RED>!=<RESET><GREEN>=<RESET>2 a<RED>===<RESET><GREEN>=<RESET>2 a<RED>!==<RESET><GREEN>=<RESET>2 a<RED>^=<RESET><GREEN>=<RESET>2 a<RED>=><RESET><GREEN>=<RESET>2
+a<RED>+=<RESET><GREEN>-=<RESET>b a<RED>*=<RESET><GREEN>%=<RESET>b a<RED>**=<RESET><GREEN>&&=<RESET>b a<RED>||=<RESET><GREEN>|=<RESET>b
+b<RED>+<RESET><GREEN>-<RESET>c a<RED>--<RESET><GREEN>++<RESET> a<RED>>><RESET><GREEN><<<RESET>b a<RED>>>><RESET><GREEN>>>>=<RESET>b a<RED>>>=<RESET><GREEN><<=<RESET>b
+a<RED>&&<RESET><GREEN>&<RESET>b a<RED>||<RESET><GREEN>|<RESET>b a<RED>&&=<RESET><GREEN>??=<RESET>b
diff --git a/t/t4034/javascript/post b/t/t4034/javascript/post
new file mode 100644
index 0000000000..46f9b627e4
--- /dev/null
+++ b/t/t4034/javascript/post
@@ -0,0 +1,33 @@
+// DecimalLiteral
+124
+0.124
+.124
+0.123e-5
+0.123E-5
+0.123E5
+12222222222222222233344445n
+// HexIntegerLiteral
+0x11
+0X5Fa1
+0x123_756
+0x1234182989812f1289bn
+// OctalIntegerLiteral
+06
+0o5
+0O4
+0511_567
+0o424242424242424242424242424242666667n
+// BinaryIntegerLiteral
+0b1101
+0B0010
+0b0001_1101_0011
+0b11111111111111000011111111111111111n
+// punctuations
+{b} (b)
+b;
+[2,3]
+[ ...params_v2 ]
+a=2 a=2 a=2 a=2 a=2 a=2 a=2 a=2
+a-=b a%=b a&&=b a|=b
+b-c a++ a<<b a>>>=b a<<=b
+a&b a|b a??=b
diff --git a/t/t4034/javascript/pre b/t/t4034/javascript/pre
new file mode 100644
index 0000000000..18f479688c
--- /dev/null
+++ b/t/t4034/javascript/pre
@@ -0,0 +1,33 @@
+// DecimalLiteral
+123
+0.123
+.123
+0.123e+5
+0.123E+5
+0.123e5
+1222222222222222223334444n
+// HexIntegerLiteral
+0x10
+0X6Fa1
+0x123_456
+0x1234182989812f1289an
+// OctalIntegerLiteral
+05
+0o6
+0O7
+0512_567
+0o424242424242424242424242424242666666n
+// BinaryIntegerLiteral
+0b1001
+0B0110
+0b0001_1001_0011
+0b1111111111111111111111111111111111111n
+// punctuations
+{a} (a)
+a;
+[1,2]
+[ 1, 2, ...params ]
+a<=2 a>=2 a==2 a!=2 a===2 a!==2 a^=2 a=>2
+a+=b a*=b a**=b a||=b
+b+c a-- a>>b a>>>b a>>=b
+a&&b a||b a&&=b
diff --git a/userdiff.c b/userdiff.c
index 8578cb0d12..306286df35 100644
--- a/userdiff.c
+++ b/userdiff.c
@@ -168,6 +168,43 @@ PATTERNS("java",
 	 "|[-+0-9.e]+[fFlL]?|0[xXbB]?[0-9a-fA-F]+[lL]?"
 	 "|[-+*/<>%&^|=!]="
 	 "|--|\\+\\+|<<=?|>>>?=?|&&|\\|\\|"),
+
+PATTERNS("javascript",
+	 /* don't match the expression may contain parenthesis, because it is not a function declaration */
+	 "!^[ \t]*(if|do|while|for|with|switch|catch|import|return)\n"
+	 /* don't match statement */
+	 "!;\n"
+	 /* match normal function or named export for function in ECMA2015 */
+	 "^((export[\t ]+)?(async[\t ]+)?function[\t ]*[\t *]*[$_[:alpha:]][$_[:alnum:]]*[\t ]*\\(.*)\n"
+	 /* match JavaScript variable declaration with a lambda expression at top level */
+	 "^((const|let|var)[\t ]*[$_[:alpha:]][$_[:alnum:]]*[\t ]*=[\t ]*"
+		"(\\(.*\\)|[$_[:alpha:]][$_[:alnum:]]*)[\t ]*=>[\t ]*\\{?)\n"
+	 /* match object's property assignment by anonymous function and CommonJS exports for named function */
+	 "^((module\\.)?[$_[:alpha:]][$_[:alnum:]]*\\.[$_[:alpha:]][$_[:alnum:]]*[\t ]*=[\t ]*(async[\t ]+)?(\\(.*\\)|[$_[:alpha:]][$_[:alnum:]]*)[\t ]*=>.*)\n"
+	 /* match assign function to LHS with explicit function keyword */
+	 "^(.*=[\t ]*function[\t ]*([$_[:alnum:]]+[\t ]*)?\\(.*)\n"
+	 /* popular unit testing framework test case pattern. Most of framework pattern is match by regex for "function in class" */
+	 "^[\t ]*(QUnit.test\\(.*)\n"
+	 /* don't match the function in class or in object literal, which has more than one ident level */
+	 "!^(\t{2,}|[ ]{5,})\n"
+	 /* match normal function in object literal */
+	 "^[\t ]*([$_[:alpha:]][$_[:alnum:]]*[\t ]*:[\t ]*function.*)\n"
+	 /* don't match chained method call */
+	 "!^[\t ]*[$_[:alpha:]][$_[:alnum:]][\t ]*\\(.*\\)\\.\n"
+	 /* match function in class and ES5 method shorthand */
+	 "^[\t ]*((static[\t ]+)?((async|get|set)[\t ]+)?[$_[:alpha:]][$_[:alnum:]]*[\t ]*\\(.*)",
+	 /* word regex */
+	 /* hexIntegerLiteral, octalIntegerLiteral, binaryIntegerLiteral, and its big version */
+	 "0[xXoObB][_0-9a-fA-F]+n?"
+	 /* DecimalLiteral and its big version*/
+	 "|[0-9][_0-9]*(\\.[0-9][_0-9]*|n)?([eE][+-]?[_0-9]+)?"
+	 "|\\.[0-9][_0-9]*([eE][+-]?[_0-9]+)?"
+	 /* punctuations */
+	 "|\\.{3}|<=|>=|==|!=|={3}|!==|\\*{2}|\\+{2}|--|<<|>>"
+	 "|>>>|&&|\\|{2}|\\?{2}|\\+=|-=|\\*=|%=|\\*{2}="
+	 "|<<=|>>=|>>>=|&=|\\|=|\\^=|&&=|\\|{2}=|\\?{2}=|=>"
+	 /* identifiers */
+	 "|[$_[:alpha:]][$_[:alnum:]]*"),
 PATTERNS("markdown",
 	 "^ {0,3}#{1,6}[ \t].*",
 	 /* -- */
