diff --git a/build-common/test/org/jetbrains/kotlin/incremental/testingUtils/classFilesComparison.kt b/build-common/test/org/jetbrains/kotlin/incremental/testingUtils/classFilesComparison.kt
index 922f9d0dfe4..8591dd23d1e 100644
--- a/build-common/test/org/jetbrains/kotlin/incremental/testingUtils/classFilesComparison.kt
+++ b/build-common/test/org/jetbrains/kotlin/incremental/testingUtils/classFilesComparison.kt
@@ -205,7 +205,7 @@ private fun kjsmToString(kjsmFile: File): String {
 }
 
 private fun sourceMapFileToString(sourceMapFile: File, generatedJsFile: File): String {
-    val sourceMapParseResult = SourceMapParser.parse(StringReader(sourceMapFile.readText()))
+    val sourceMapParseResult = SourceMapParser.parse(sourceMapFile.readText())
     return when (sourceMapParseResult) {
         is SourceMapSuccess -> {
             val bytesOut = ByteArrayOutputStream()
diff --git a/compiler/cli/cli-js/src/org/jetbrains/kotlin/cli/js/dce/K2JSDce.kt b/compiler/cli/cli-js/src/org/jetbrains/kotlin/cli/js/dce/K2JSDce.kt
index 5f2c50869e7..0a44a8e85e5 100644
--- a/compiler/cli/cli-js/src/org/jetbrains/kotlin/cli/js/dce/K2JSDce.kt
+++ b/compiler/cli/cli-js/src/org/jetbrains/kotlin/cli/js/dce/K2JSDce.kt
@@ -122,7 +122,7 @@ class K2JSDce : CLITool<K2JSDceArguments>() {
 
     private fun mapSourcePaths(inputFile: File, targetFile: File): Boolean {
         val json = try {
-            InputStreamReader(FileInputStream(inputFile), "UTF-8").use { parseJson(it) }
+            parseJson(inputFile)
         } catch (e: JsonSyntaxException) {
             return false
         }
diff --git a/compiler/cli/cli-js/src/org/jetbrains/kotlin/cli/js/internal/JSStdlibLinker.kt b/compiler/cli/cli-js/src/org/jetbrains/kotlin/cli/js/internal/JSStdlibLinker.kt
index efb4d2c1df5..c9cfdd23a6c 100644
--- a/compiler/cli/cli-js/src/org/jetbrains/kotlin/cli/js/internal/JSStdlibLinker.kt
+++ b/compiler/cli/cli-js/src/org/jetbrains/kotlin/cli/js/internal/JSStdlibLinker.kt
@@ -52,7 +52,7 @@ private fun mergeStdlibParts(outputFile: File, wrapperFile: File, baseDir: File,
 
         val sourceMapFile = File(file.parent, file.name + ".map")
         if (sourceMapFile.exists()) {
-            val sourceMapParse = sourceMapFile.reader().use { SourceMapParser.parse(it) }
+            val sourceMapParse = SourceMapParser.parse(sourceMapFile)
             when (sourceMapParse) {
                 is SourceMapError -> {
                     System.err.println("Error parsing source map file $sourceMapFile: ${sourceMapParse.message}")
@@ -82,7 +82,7 @@ private fun mergeStdlibParts(outputFile: File, wrapperFile: File, baseDir: File,
 
     outputFile.writeText(programText + "\n//# sourceMappingURL=${sourceMapFile.name}\n")
 
-    val sourceMapJson = StringReader(sourceMapContent).use { parseJson(it) }
+    val sourceMapJson = parseJson(sourceMapContent)
     val sources = (sourceMapJson as JsonObject).properties["sources"] as JsonArray
 
     sourceMapJson.properties["sourcesContent"] = JsonArray(*sources.elements.map { sourcePath ->
diff --git a/js/js.dce/src/org/jetbrains/kotlin/js/dce/DeadCodeElimination.kt b/js/js.dce/src/org/jetbrains/kotlin/js/dce/DeadCodeElimination.kt
index 136c629f011..3e1c56a526d 100644
--- a/js/js.dce/src/org/jetbrains/kotlin/js/dce/DeadCodeElimination.kt
+++ b/js/js.dce/src/org/jetbrains/kotlin/js/dce/DeadCodeElimination.kt
@@ -89,8 +89,7 @@ class DeadCodeElimination(private val logConsumer: (DCELogLevel, String) -> Unit
                     return@map block
                 }
                 val sourceMapParse = file.sourceMapResource
-                        ?.let { InputStreamReader(it.reader(), "UTF-8") }
-                        ?.use { SourceMapParser.parse(it) }
+                        ?.let { SourceMapParser.parse(InputStreamReader(it.reader(), "UTF-8").readText()) }
                 when (sourceMapParse) {
                     is SourceMapError -> {
                         logConsumer(
diff --git a/js/js.inliner/src/org/jetbrains/kotlin/js/inline/FunctionReader.kt b/js/js.inliner/src/org/jetbrains/kotlin/js/inline/FunctionReader.kt
index 83686c88714..c4f830c159b 100644
--- a/js/js.inliner/src/org/jetbrains/kotlin/js/inline/FunctionReader.kt
+++ b/js/js.inliner/src/org/jetbrains/kotlin/js/inline/FunctionReader.kt
@@ -114,7 +114,7 @@ class FunctionReader(
                 }
 
                 val sourceMap = sourceMapContent?.let {
-                    val sourceMapResult = SourceMapParser.parse(StringReader(it))
+                    val sourceMapResult = SourceMapParser.parse(it)
                     when (sourceMapResult) {
                         is SourceMapSuccess -> sourceMapResult.value
                         is SourceMapError -> {
diff --git a/js/js.parser/src/org/jetbrains/kotlin/js/parser/sourcemaps/JSON.kt b/js/js.parser/src/org/jetbrains/kotlin/js/parser/sourcemaps/JSON.kt
index 441fc8197b9..e6c73422e4e 100644
--- a/js/js.parser/src/org/jetbrains/kotlin/js/parser/sourcemaps/JSON.kt
+++ b/js/js.parser/src/org/jetbrains/kotlin/js/parser/sourcemaps/JSON.kt
@@ -16,10 +16,7 @@
 
 package org.jetbrains.kotlin.js.parser.sourcemaps
 
-import java.io.Reader
-import java.io.StringReader
-import java.io.StringWriter
-import java.io.Writer
+import java.io.*
 
 sealed class JsonNode {
     abstract fun write(writer: Writer)
@@ -120,8 +117,7 @@ data class JsonNumber(val value: Double) : JsonNode() {
     override fun write(writer: Writer) {
         if (value.toLong().toDouble() == value) {
             writer.append(value.toLong().toString())
-        }
-        else {
+        } else {
             writer.append(value.toString())
         }
     }
@@ -130,14 +126,15 @@ data class JsonNumber(val value: Double) : JsonNode() {
 }
 
 class JsonSyntaxException(val offset: Int, val line: Int, val column: Int, val text: String) :
-        RuntimeException("JSON syntax error at ${line + 1}, ${column + 1}: $text")
+    RuntimeException("JSON syntax error at ${line + 1}, ${column + 1}: $text")
 
-fun parseJson(reader: Reader): JsonNode = JsonParser(reader).parse()
+fun parseJson(file: File): JsonNode = parseJson(file.readText(Charsets.UTF_8))
 
-fun parseJson(text: String): JsonNode = parseJson(StringReader(text))
+fun parseJson(text: String): JsonNode = JsonParser(text).parse()
 
-private class JsonParser(val reader: Reader) {
-    private var charCode = reader.read()
+private class JsonParser(val content: String) {
+    private var index = 0
+    private var charCode = content.getOrNull(index++)?.toInt() ?: -1
     private var offset = 0
     private var line = 0
     private var col = 0
@@ -165,13 +162,27 @@ private class JsonParser(val reader: Reader) {
             '['.toInt() -> parseArray()
             '{'.toInt() -> parseObject()
             '"'.toInt() -> JsonString(parseString())
-            'n'.toInt() -> { expectString("null"); JsonNull }
-            'f'.toInt() -> { expectString("false"); JsonBoolean.FALSE }
-            't'.toInt() -> { expectString("true"); JsonBoolean.TRUE }
-            in '0'.toInt()..'9'.toInt() -> JsonNumber(parseNumber())
-            '-'.toInt() -> { advance(); JsonNumber(-parseNumber())
+            'n'.toInt() -> {
+                expectString("null")
+                JsonNull
+            }
+            'f'.toInt() -> {
+                expectString("false")
+                JsonBoolean.FALSE
+            }
+            't'.toInt() -> {
+                expectString("true")
+                JsonBoolean.TRUE
+            }
+            '-'.toInt() -> {
+                advance()
+                JsonNumber(-parseNumber())
+            }
+            else -> if (charCode in '0'.toInt()..'9'.toInt()) {
+                JsonNumber(parseNumber())
+            } else {
+                error("Unexpected char")
             }
-            else -> error("Unexpected char")
         }
     }
 
@@ -183,8 +194,7 @@ private class JsonParser(val reader: Reader) {
             if (charCode == ']'.toInt()) {
                 advance()
                 break
-            }
-            else {
+            } else {
                 if (result.elements.isNotEmpty()) {
                     expectCharAndAdvance(',')
                 }
@@ -202,8 +212,7 @@ private class JsonParser(val reader: Reader) {
             if (charCode == '}'.toInt()) {
                 advance()
                 break
-            }
-            else {
+            } else {
                 if (result.properties.isNotEmpty()) {
                     expectCharAndAdvance(',')
                 }
@@ -356,7 +365,7 @@ private class JsonParser(val reader: Reader) {
                 wasCR = false
             }
         }
-        charCode = reader.read()
+        charCode = content.getOrNull(index++)?.toInt() ?: -1
         offset++
     }
 
diff --git a/js/js.parser/src/org/jetbrains/kotlin/js/parser/sourcemaps/SourceMapParser.kt b/js/js.parser/src/org/jetbrains/kotlin/js/parser/sourcemaps/SourceMapParser.kt
index 56102ae8254..ac602ba3271 100644
--- a/js/js.parser/src/org/jetbrains/kotlin/js/parser/sourcemaps/SourceMapParser.kt
+++ b/js/js.parser/src/org/jetbrains/kotlin/js/parser/sourcemaps/SourceMapParser.kt
@@ -16,20 +16,29 @@
 
 package org.jetbrains.kotlin.js.parser.sourcemaps
 
+import java.io.File
 import java.io.IOException
-import java.io.Reader
 import java.io.StringReader
 
 object SourceMapParser {
     @Throws(IOException::class)
-    fun parse(reader: Reader): SourceMapParseResult {
+    fun parse(file: File): SourceMapParseResult {
+        return parse(file.readText(Charsets.UTF_8))
+    }
+
+    @Throws(IOException::class)
+    fun parse(content: String): SourceMapParseResult {
         val jsonObject = try {
-            parseJson(reader)
+            parseJson(content)
         }
         catch (e: JsonSyntaxException) {
             return SourceMapError(e.message ?: "parse error")
         }
+        return parse(jsonObject)
+    }
 
+    @Throws(IOException::class)
+    private fun parse(jsonObject: JsonNode): SourceMapParseResult {
         if (jsonObject !is JsonObject) return SourceMapError("Top-level object expected")
 
         val version = jsonObject.properties["version"] ?: return SourceMapError("Version not defined")
diff --git a/js/js.tests/test/org/jetbrains/kotlin/js/test/BasicBoxTest.kt b/js/js.tests/test/org/jetbrains/kotlin/js/test/BasicBoxTest.kt
index b43e58086ad..585b1baef21 100644
--- a/js/js.tests/test/org/jetbrains/kotlin/js/test/BasicBoxTest.kt
+++ b/js/js.tests/test/org/jetbrains/kotlin/js/test/BasicBoxTest.kt
@@ -420,8 +420,8 @@ abstract class BasicBoxTest(
         val recompiledSourceMap = removeRecompiledSuffix(
                 FileUtil.loadFile(File(recompiledOutputFile.parentFile, recompiledOutputFile.name + ".map")))
         if (originalSourceMap != recompiledSourceMap) {
-            val originalSourceMapParse = SourceMapParser.parse(StringReader(originalSourceMap))
-            val recompiledSourceMapParse = SourceMapParser.parse(StringReader(recompiledSourceMap))
+            val originalSourceMapParse = SourceMapParser.parse(originalSourceMap)
+            val recompiledSourceMapParse = SourceMapParser.parse(recompiledSourceMap)
             if (originalSourceMapParse is SourceMapSuccess && recompiledSourceMapParse is SourceMapSuccess) {
                 assertEquals("Source map file changed after recompilation",
                              originalSourceMapParse.toDebugString(),
@@ -570,7 +570,7 @@ abstract class BasicBoxTest(
         val parsedProgram = JsProgram()
         parsedProgram.globalBlock.statements += parse(code, ThrowExceptionOnErrorReporter, parsedProgram.scope, outputFile.path).orEmpty()
         removeLocationFromBlocks(parsedProgram)
-        val sourceMapParseResult = SourceMapParser.parse(StringReader(generatedSourceMap))
+        val sourceMapParseResult = SourceMapParser.parse(generatedSourceMap)
         val sourceMap = when (sourceMapParseResult) {
             is SourceMapSuccess -> sourceMapParseResult.value
             is SourceMapError -> error("Could not parse source map: ${sourceMapParseResult.message}")