diff --git a/js/js.frontend/src/org/jetbrains/kotlin/js/naming/NameSuggestion.kt b/js/js.frontend/src/org/jetbrains/kotlin/js/naming/NameSuggestion.kt
index 2fdcd368660..d5d37886a28 100644
--- a/js/js.frontend/src/org/jetbrains/kotlin/js/naming/NameSuggestion.kt
+++ b/js/js.frontend/src/org/jetbrains/kotlin/js/naming/NameSuggestion.kt
@@ -360,27 +360,54 @@ class NameSuggestion {
     }
 }
 
+private fun Char.isAllowedLatinLetterOrSpecial(): Boolean {
+    return this in 'a'..'z' || this in 'A'..'Z' || this == '_' || this == '$'
+}
+
+private fun Char.isAllowedSimpleDigit() =
+    this in '0'..'9'
+
+private fun Char.isNotAllowedSimpleCharacter() = when (this) {
+    ' ', '<', '>', '-', '?' -> true
+    else -> false
+}
+
+fun Char.isES5IdentifierStart(): Boolean {
+    if (isAllowedLatinLetterOrSpecial()) return true
+    if (isNotAllowedSimpleCharacter()) return false
+
+    return isES5IdentifierStartFull()
+}
+
 // See ES 5.1 spec: https://www.ecma-international.org/ecma-262/5.1/#sec-7.6
-fun Char.isES5IdentifierStart() =
-        Character.isLetter(this) ||   // Lu | Ll | Lt | Lm | Lo
-        Character.getType(this).toByte() == Character.LETTER_NUMBER ||
-        // Nl which is missing in Character.isLetter, but present in UnicodeLetter in spec
-        this == '_' ||
-        this == '$'
+private fun Char.isES5IdentifierStartFull() =
+    Character.isLetter(this) ||   // Lu | Ll | Lt | Lm | Lo
+            // Nl which is missing in Character.isLetter, but present in UnicodeLetter in spec
+            Character.getType(this).toByte() == Character.LETTER_NUMBER
 
-fun Char.isES5IdentifierPart() =
-        isES5IdentifierStart() ||
-        when (Character.getType(this).toByte()) {
-            Character.NON_SPACING_MARK,
-            Character.COMBINING_SPACING_MARK,
-            Character.DECIMAL_DIGIT_NUMBER,
-            Character.CONNECTOR_PUNCTUATION -> true
-            else -> false
-        } ||
-        this == '\u200C' ||   // Zero-width non-joiner
-        this == '\u200D'      // Zero-width joiner
 
-fun String.isValidES5Identifier() =
-        isNotEmpty() &&
-        first().isES5IdentifierStart() &&
-        drop(1).all { it.isES5IdentifierPart() }
+fun Char.isES5IdentifierPart(): Boolean {
+    if (isAllowedLatinLetterOrSpecial()) return true
+    if (isAllowedSimpleDigit()) return true
+    if (isNotAllowedSimpleCharacter()) return false
+
+    return isES5IdentifierStartFull() ||
+            when (Character.getType(this).toByte()) {
+                Character.NON_SPACING_MARK,
+                Character.COMBINING_SPACING_MARK,
+                Character.DECIMAL_DIGIT_NUMBER,
+                Character.CONNECTOR_PUNCTUATION -> true
+                else -> false
+            } ||
+            // Nl which is missing in Character.isLetter, but present in UnicodeLetter in spec
+            this == '\u200C' ||   // Zero-width non-joiner
+            this == '\u200D'      // Zero-width joiner
+}
+
+fun String.isValidES5Identifier(): Boolean {
+    if (isEmpty() || !this[0].isES5IdentifierStart()) return false
+    for (idx in 1 ..length-1) {
+        if (!get(idx).isES5IdentifierPart()) return false
+    }
+    return true
+}
\ No newline at end of file