diff --git a/compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/CommonBackendContext.kt b/compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/CommonBackendContext.kt
index 62f7114cbe4..e28df0b9866 100644
--- a/compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/CommonBackendContext.kt
+++ b/compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/CommonBackendContext.kt
@@ -33,4 +33,6 @@ interface CommonBackendContext : BackendContext, LoggingContext {
             putValueArgument(0, builder.irString(name))
         }
     }
+
+    val mapping: Mapping
 }
diff --git a/compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/Mappings.kt b/compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/Mappings.kt
new file mode 100644
index 00000000000..71dde7a7eea
--- /dev/null
+++ b/compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/Mappings.kt
@@ -0,0 +1,58 @@
+/*
+ * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.backend.common
+
+import org.jetbrains.kotlin.ir.declarations.IrDeclaration
+import org.jetbrains.kotlin.ir.declarations.IrFunction
+import kotlin.reflect.KMutableProperty0
+import kotlin.reflect.KProperty
+
+interface Mapping {
+    val defaultArgumentsDispatchFunction: Delegate<IrFunction, IrFunction>
+    val defaultArgumentsOriginalFunction: Delegate<IrFunction, IrFunction>
+
+    abstract class Delegate<K : IrDeclaration, V> {
+        abstract operator fun get(key: K): V?
+
+        abstract operator fun set(key: K, value: V?)
+
+        operator fun getValue(thisRef: K, desc: KProperty<*>): V? = get(thisRef)
+
+        operator fun setValue(thisRef: K, desc: KProperty<*>, value: V?) {
+            set(thisRef, value)
+        }
+    }
+}
+
+open class DefaultMapping : Mapping {
+
+    override val defaultArgumentsDispatchFunction: Mapping.Delegate<IrFunction, IrFunction> = newMapping()
+    override val defaultArgumentsOriginalFunction: Mapping.Delegate<IrFunction, IrFunction> = newMapping()
+
+    protected fun <K : IrDeclaration, V> newMapping() = object : Mapping.Delegate<K, V>() {
+        private val map: MutableMap<K, V> = mutableMapOf()
+
+        override operator fun get(key: K): V? {
+            return map[key]
+        }
+
+        override operator fun set(key: K, value: V?) {
+            if (value == null) {
+                map.remove(key)
+            } else {
+                map[key] = value
+            }
+        }
+    }
+}
+
+fun <V : Any> KMutableProperty0<V?>.getOrPut(fn: () -> V) = this.get() ?: fn().also {
+    this.set(it)
+}
+
+fun <K : IrDeclaration, V> Mapping.Delegate<K, V>.getOrPut(key: K, fn: () -> V) = this[key] ?: fn().also {
+    this[key] = it
+}
\ No newline at end of file
diff --git a/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/JsCommonBackendContext.kt b/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/JsCommonBackendContext.kt
new file mode 100644
index 00000000000..d948afa1bdc
--- /dev/null
+++ b/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/JsCommonBackendContext.kt
@@ -0,0 +1,12 @@
+/*
+ * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.ir.backend.js
+
+import org.jetbrains.kotlin.backend.common.CommonBackendContext
+
+interface JsCommonBackendContext : CommonBackendContext {
+    override val mapping: JsMapping
+}
\ No newline at end of file
diff --git a/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/JsDeclarationFactory.kt b/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/JsDeclarationFactory.kt
index 4a625045aae..94ddd4dd03f 100644
--- a/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/JsDeclarationFactory.kt
+++ b/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/JsDeclarationFactory.kt
@@ -5,6 +5,7 @@
 
 package org.jetbrains.kotlin.backend.js
 
+import org.jetbrains.kotlin.backend.common.getOrPut
 import org.jetbrains.kotlin.backend.common.ir.DeclarationFactory
 import org.jetbrains.kotlin.backend.common.ir.copyTo
 import org.jetbrains.kotlin.backend.common.ir.copyTypeParametersFrom
@@ -12,6 +13,7 @@ import org.jetbrains.kotlin.descriptors.ClassKind
 import org.jetbrains.kotlin.descriptors.Visibilities
 import org.jetbrains.kotlin.descriptors.Visibility
 import org.jetbrains.kotlin.ir.UNDEFINED_OFFSET
+import org.jetbrains.kotlin.ir.backend.js.JsMapping
 import org.jetbrains.kotlin.ir.backend.js.ir.JsIrBuilder
 import org.jetbrains.kotlin.ir.backend.js.utils.Namer
 import org.jetbrains.kotlin.ir.declarations.*
@@ -25,12 +27,11 @@ import org.jetbrains.kotlin.ir.types.IrType
 import org.jetbrains.kotlin.ir.util.defaultType
 import org.jetbrains.kotlin.ir.util.dump
 import org.jetbrains.kotlin.name.Name
-import java.util.*
 
-class JsDeclarationFactory : DeclarationFactory {
-    private val singletonFieldDescriptors = HashMap<IrClass, IrField>()
-    private val outerThisFieldSymbols = HashMap<IrClass, IrField>()
-    private val innerClassConstructors = HashMap<IrConstructor, IrConstructor>()
+class JsDeclarationFactory(mapping: JsMapping) : DeclarationFactory {
+    private val singletonFieldDescriptors = mapping.singletonFieldDescriptors
+    private val outerThisFieldSymbols = mapping.outerThisFieldSymbols
+    private val innerClassConstructors = mapping.innerClassConstructors
 
     override fun getFieldForEnumEntry(enumEntry: IrEnumEntry): IrField = TODO()
 
diff --git a/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/JsIrBackendContext.kt b/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/JsIrBackendContext.kt
index ef67fb1ab69..4c58afa774c 100644
--- a/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/JsIrBackendContext.kt
+++ b/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/JsIrBackendContext.kt
@@ -5,7 +5,6 @@
 
 package org.jetbrains.kotlin.ir.backend.js
 
-import org.jetbrains.kotlin.backend.common.CommonBackendContext
 import org.jetbrains.kotlin.backend.common.atMostOne
 import org.jetbrains.kotlin.backend.common.ir.Ir
 import org.jetbrains.kotlin.backend.common.ir.Symbols
@@ -47,7 +46,7 @@ class JsIrBackendContext(
     val additionalExportedDeclarations: Set<FqName>,
     override val configuration: CompilerConfiguration, // TODO: remove configuration from backend context
     override val scriptMode: Boolean = false
-) : CommonBackendContext {
+) : JsCommonBackendContext {
     override val transformedFunction = mutableMapOf<IrFunctionSymbol, IrSimpleFunctionSymbol>()
     override val lateinitNullableFields = mutableMapOf<IrField, IrField>()
 
@@ -102,7 +101,9 @@ class JsIrBackendContext(
         }
 
     override val sharedVariablesManager = JsSharedVariablesManager(irBuiltIns, implicitDeclarationFile)
-    override val declarationFactory = JsDeclarationFactory()
+
+    override val mapping = JsMapping()
+    override val declarationFactory = JsDeclarationFactory(mapping)
 
     companion object {
         val KOTLIN_PACKAGE_FQN = FqName.fromSegments(listOf("kotlin"))
diff --git a/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/JsMapping.kt b/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/JsMapping.kt
new file mode 100644
index 00000000000..9723c46925c
--- /dev/null
+++ b/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/JsMapping.kt
@@ -0,0 +1,17 @@
+/*
+ * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.ir.backend.js
+
+import org.jetbrains.kotlin.backend.common.DefaultMapping
+import org.jetbrains.kotlin.ir.declarations.IrClass
+import org.jetbrains.kotlin.ir.declarations.IrConstructor
+import org.jetbrains.kotlin.ir.declarations.IrField
+
+class JsMapping : DefaultMapping() {
+    val singletonFieldDescriptors = newMapping<IrClass, IrField>()
+    val outerThisFieldSymbols = newMapping<IrClass, IrField>()
+    val innerClassConstructors = newMapping<IrConstructor, IrConstructor>()
+}
\ No newline at end of file
diff --git a/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/JvmBackendContext.kt b/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/JvmBackendContext.kt
index ed12a4c1949..61eb0794f24 100644
--- a/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/JvmBackendContext.kt
+++ b/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/JvmBackendContext.kt
@@ -6,6 +6,8 @@
 package org.jetbrains.kotlin.backend.jvm
 
 import org.jetbrains.kotlin.backend.common.CommonBackendContext
+import org.jetbrains.kotlin.backend.common.DefaultMapping
+import org.jetbrains.kotlin.backend.common.Mapping
 import org.jetbrains.kotlin.backend.common.ir.Ir
 import org.jetbrains.kotlin.backend.common.lower.irThrow
 import org.jetbrains.kotlin.backend.common.phaser.PhaseConfig
@@ -68,6 +70,8 @@ class JvmBackendContext(
     override val declarationFactory: JvmDeclarationFactory = JvmDeclarationFactory(methodSignatureMapper)
     override val sharedVariablesManager = JvmSharedVariablesManager(state.module, builtIns, irBuiltIns)
 
+    override val mapping: Mapping = DefaultMapping()
+
     val psiErrorBuilder = PsiErrorBuilder(psiSourceManager, state.diagnostics)
 
     override val ir = JvmIr(irModuleFragment, this.symbolTable)
diff --git a/compiler/ir/backend.wasm/src/org/jetbrains/kotlin/backend/wasm/WasmBackendContext.kt b/compiler/ir/backend.wasm/src/org/jetbrains/kotlin/backend/wasm/WasmBackendContext.kt
index 8853a495d2e..85e395cfa40 100644
--- a/compiler/ir/backend.wasm/src/org/jetbrains/kotlin/backend/wasm/WasmBackendContext.kt
+++ b/compiler/ir/backend.wasm/src/org/jetbrains/kotlin/backend/wasm/WasmBackendContext.kt
@@ -5,7 +5,6 @@
 
 package org.jetbrains.kotlin.backend.wasm
 
-import org.jetbrains.kotlin.backend.common.CommonBackendContext
 import org.jetbrains.kotlin.backend.common.ir.Ir
 import org.jetbrains.kotlin.backend.common.ir.Symbols
 import org.jetbrains.kotlin.backend.js.JsDeclarationFactory
@@ -14,6 +13,8 @@ import org.jetbrains.kotlin.descriptors.ModuleDescriptor
 import org.jetbrains.kotlin.descriptors.PackageFragmentDescriptor
 import org.jetbrains.kotlin.descriptors.impl.EmptyPackageFragmentDescriptor
 import org.jetbrains.kotlin.ir.IrElement
+import org.jetbrains.kotlin.ir.backend.js.JsCommonBackendContext
+import org.jetbrains.kotlin.ir.backend.js.JsMapping
 import org.jetbrains.kotlin.ir.backend.js.JsSharedVariablesManager
 import org.jetbrains.kotlin.ir.declarations.*
 import org.jetbrains.kotlin.ir.declarations.impl.IrExternalPackageFragmentImpl
@@ -34,7 +35,7 @@ class WasmBackendContext(
     irModuleFragment: IrModuleFragment,
     val additionalExportedDeclarations: Set<FqName>,
     override val configuration: CompilerConfiguration
-) : CommonBackendContext {
+) : JsCommonBackendContext {
     override val builtIns = module.builtIns
     override var inVerbosePhase: Boolean = false
     override val scriptMode = false
@@ -49,7 +50,9 @@ class WasmBackendContext(
         )
     }
 
-    override val declarationFactory = JsDeclarationFactory()
+    override val mapping = JsMapping()
+
+    override val declarationFactory = JsDeclarationFactory(mapping)
 
     val objectToGetInstanceFunction = mutableMapOf<IrClassSymbol, IrSimpleFunction>()
     override val internalPackageFqn = FqName("kotlin.wasm")