add beforeMatch handler

docs/reference.md

@@ -10,6 +10,7 @@
     * [`defaultValue`](#defaultvalue)
     * [`ignoreUnknown`](#ignoreunknown)
     * [`childKey`](#childkey)
+    * [`beforeMatch`](#beforematch)
     * [`onUnmatch`](#onunmatch)
     * [`serializer`](#serializer)
     * [`deserializer`](#deserializer)
@@ -77,6 +78,7 @@ const Options = struct({
   defaultValue: 'any',
   ignoreUnknown: 'boolean',
   childKey: 'string',
+  beforeMatch: 'function',
   onUnmatch: 'function',
   serializer: 'function',
   deserializer: 'function'
@@ -94,6 +96,9 @@ Decide if current node should be ignored when no rule is matched, `false` by def
 #### `childKey`
 Key string referencing children of a node. `'children'` by default.
 
+#### `beforeMatch`
+Called before matching rules for current node. This handler does not affect subsequent traversing. `(node) => {}` by default.
+
 #### `onUnmatch`
 Called when no rule is found for current node and `ignoreKnown === false`. This handler does not affect subsequent traversing. `(node) => {}` by default.
 

src/bumpover/index.js

@@ -18,6 +18,7 @@ export class Bumpover {
       defaultValue: null,
       ignoreUnknown: false,
       childKey: 'children',
+      beforeMatch: node => {},
       onUnmatch: node => {},
       serializer: a => a,
       deserializer: a => a,
@@ -33,10 +34,11 @@ export class Bumpover {
       return
     }
     const { rules, options, bumpNode } = this
+    const { ignoreUnknown, onUnmatch, beforeMatch } = options
+    beforeMatch(node)
     const rule = getRule(node, rules)
     // Keep or discard unknown node according to `ignoreUnknown` option.
     if (!rule) {
-      const { ignoreUnknown, onUnmatch } = options
       if (ignoreUnknown) {
         bumpIgnoredNode(node, options, bumpNode, resolve, reject)
         return
@@ -68,20 +70,22 @@ export class Bumpover {
     try { Rules(rules) } catch (e) { reject(e) }
     try { Options(options) } catch (e) { reject(e) }
 
-    const { defaultValue, deserializer, ignoreUnknown } = options
+    const {
+      defaultValue, deserializer, ignoreUnknown, beforeMatch, onUnmatch
+    } = options
     // Update root node with rules.
     const rootNode = deserializer(input)
     if (!rootNode) {
       resolve(defaultValue)
       return
     }
-
+    beforeMatch(rootNode)
     const rule = getRule(rootNode, rules)
     // Resolve default value if root node is unknown.
     if (!rule) {
       if (ignoreUnknown) resolve(defaultValue)
       else {
-        this.options.onUnmatch(rootNode)
+        onUnmatch(rootNode)
         bumpRoot(rootNode, [], options, bumpNode, resolve, reject)
       }
     } else {

src/options.js

@@ -4,6 +4,7 @@ export const Options = struct({
   defaultValue: 'any',
   ignoreUnknown: 'boolean',
   childKey: 'string',
+  beforeMatch: 'function',
   onUnmatch: 'function',
   serializer: 'function',
   deserializer: 'function'