Add skipValidation option to .load()

Author: jhlywa

Diff for: README.md

@@ -527,7 +527,7 @@ chess.isThreefoldRepetition()
 // -> true
 ```
 
-### .load(fen: string, { preserveHeaders = false } = {})
+### .load(fen: string, { skipValidation = false, preserveHeaders = false } = {})
 
 Clears the board and loads the provided FEN string. The castling rights, en
 passant square and move numbers are defaulted to `- - 0 1` if omitted. Throws an
@@ -538,11 +538,14 @@ const chess = new Chess()
 chess.load('4r3/8/2p2PPk/1p6/pP2p1R1/P1B5/2P2K2/3r4 w - - 1 45')
 
 try {
-  chess.load('4r3/8/X12XPk/1p6/pP2p1R1/P1B5/2P2K2/3r4 w - - 1 45')
+  chess.load('8/4p3/8/8/8/8/4P3/6K1 w - - 1 45')
 } catch (e) {
   console.log(e)
 }
-// -> Error: Invalid FEN: piece data is invalid (invalid piece)
+// -> Error: Invalid FEN: missing black king
+
+chess.load('8/4p3/8/8/8/8/4P3/6K1 w - - 1 45', { skipValidation: true })
+// -> Works!
 ```
 
 ### .loadPgn(pgn, [ options ])

Diff for: __tests__/load.test.ts

@@ -31,6 +31,18 @@ test('load - bad piece (X)', () => {
   expect(() => chess.load(fen)).toThrow()
 })
 
+test('load - missing white king', () => {
+  const chess = new Chess()
+  const fen = '1nbqkbn1/pppp1ppp/8/4p3/4P3/8/PPPP1PPP/1NBQ1BN1 b - - 1 2'
+  expect(() => chess.load(fen)).toThrow()
+})
+
+test('load - missing black king', () => {
+  const chess = new Chess()
+  const fen = '1nbq1bn1/pppp1ppp/8/4p3/4P3/8/PPPP1PPP/1NBQKBN1 b - - 1 2'
+  expect(() => chess.load(fen)).toThrow()
+})
+
 test('load - bad ep square (e9)', () => {
   const chess = new Chess()
   const fen = 'rnbqkbnr/pppppppp/8/8/4P3/8/PPPP1PPP/RNBQKBNR b KQkq e9 0 1'
@@ -61,3 +73,10 @@ test('load - preserveHeaders = true', () => {
     Black: 'Viswanathan Anand',
   })
 })
+
+test('load - skipValidation = true', () => {
+  const chess = new Chess()
+  // missing white king
+  const fen = '1nbqkbn1/pppp1ppp/8/4p3/4P3/8/PPPP1PPP/1NBQ1BN1 b - - 1 2'
+  expect(() => chess.load(fen, { skipValidation: true })).not.toThrow()
+})

Diff for: src/chess.ts

@@ -598,7 +598,7 @@ export class Chess {
     }
   }
 
-  load(fen: string, { preserveHeaders = false } = {}) {
+  load(fen: string, { skipValidation = false, preserveHeaders = false } = {}) {
     let tokens = fen.split(/\s+/)
 
     // append commonly omitted fen tokens
@@ -609,9 +609,11 @@ export class Chess {
 
     tokens = fen.split(/\s+/)
 
-    const { ok, error } = validateFen(fen)
-    if (!ok) {
-      throw new Error(error)
+    if (!skipValidation) {
+      const { ok, error } = validateFen(fen)
+      if (!ok) {
+        throw new Error(error)
+      }
     }
 
     const position = tokens[0]