Ensure that js regex also works when using js obfuscator/compator

Author: untoldwind

src/jsMain/kotlin/com/github/h0tk3y/betterParse/lexer/RegexToken.kt

@@ -1,49 +1,29 @@
 package com.github.h0tk3y.betterParse.lexer
 
-import kotlin.js.RegExp
-
 public actual class RegexToken : Token {
   private val pattern: String
   private val regex: Regex
 
-  /**
-   * To ensure that the [regex] will only match its pattern from the index where it is called on
-   * with Regex.find(input, startIndex), set the JS RegExp flag 'y', which makes the RegExp
-   * 'sticky'. See: https://javascript.info/regexp-sticky
-   */
-  private fun preprocessRegex(regex: Regex) {
-    val possibleNames = listOf("nativePattern_1", "nativePattern_0", "_nativePattern")
-    for (name in possibleNames) {
-      val r = regex.asDynamic()[name]
-      if (jsTypeOf(r) !== "undefined" && r !== null) {
-        val src = r.source as String
-        val flags = r.flags as String + if (r.sticky as Boolean) "" else "y"
-        regex.asDynamic()[name] = RegExp(src, flags)
-        break
-      }
-    }
-  }
-
   public actual constructor(
       name: String?,
       patternString: String,
       ignored: Boolean
   ) : super(name, ignored) {
     pattern = patternString
     regex = pattern.toRegex()
-    preprocessRegex(regex)
   }
 
   public actual constructor(name: String?, regex: Regex, ignored: Boolean) : super(name, ignored) {
     pattern = regex.pattern
     this.regex = regex
-    preprocessRegex(regex)
   }
 
   override actual fun match(input: CharSequence, fromIndex: Int): Int =
       regex.find(input, fromIndex)?.range?.let {
-        val length = it.last - it.first + 1
-        length
+        if (it.first == fromIndex) {
+          val length = it.last - it.first + 1
+          length
+        } else 0
       } ?: 0
 
   override fun toString(): String = "${name ?: ""} [$pattern]" + if (ignored) " [ignorable]" else ""