Improved performance of "$" on jsonnode

lib/pure/json.nim

@@ -949,10 +949,50 @@ proc pretty*(node: JsonNode, indent = 2): string =
   result = ""
   toPretty(result, node, indent)
 
+proc toUgly*(result: var string, node: JsonNode) =
+  ## Converts `node` to its JSON Representation, without
+  ## regard for human redability.
+  var comma = false
+  case node.kind:
+  of JArray:
+      result.add "["
+      for child in node.elems:
+          if comma: result.add ","
+          else:     comma = true
+          result.toUgly child
+      result.add "]"
+  of JObject:
+      result.add "{"
+      for key, value in items(node.fields):
+          if comma: result.add ","
+          else:     comma = true
+          result.add "\""
+          result.add key.escapeJson()
+          result.add "\":"
+          result.toUgly value
+      result.add "}"
+  of JString:
+      result.add "\""
+      result.add node.str.escapeJson()
+      result.add "\""
+  of JInt:
+      result.add($node.num)
+  of JFloat:
+      result.add($node.fnum)
+  of JBool:
+      result.add(if node.bval: "true" else: "false")
+  of JNull:
+      result.add "null"
+
+proc toUgly*(node: JsonNode): string =
+  ## Converts `node` to its JSON Representation on one line.
+  result = newStringOfCap(node.len shl 1)
+  toUgly(result, node)
+
 proc `$`*(node: JsonNode): string =
   ## Converts `node` to its JSON Representation on one line.
-  result = ""
-  toPretty(result, node, 0, false)
+  result = newStringOfCap(node.len shl 1)
+  toUgly(result, node)
 
 iterator items*(node: JsonNode): JsonNode =
   ## Iterator for the items of `node`. `node` has to be a JArray.