Script().fromString(str)

...the format of fromString and toString are deliberately not compatible with
bitcoind. The format here is supposed to be both human-readable, and
byte-for-byte isomorphic to the binary representation. In the future we will
need to add support for bitcoind-like strings, both for the test data (e.g.,
script_invalid.json) or for the bitcoind console style.

lib/script.js

@@ -105,6 +105,44 @@ Script.prototype.toBuffer = function() {
   return bw.concat();
 };
 
+Script.prototype.fromString = function(str) {
+  this.chunks = [];
+
+  var tokens = str.split(' ');
+  var i = 0;
+  while (i < tokens.length) {
+    var token = tokens[i];
+    var opcode = Opcode(token);
+    var opcodenum = opcode.toNumber();
+
+    if (typeof opcodenum === 'undefined') {
+      opcodenum = parseInt(token);
+      if (opcodenum > 0 && opcodenum < Opcode.map.OP_PUSHDATA1) {
+        this.chunks.push({
+          buf: new Buffer(tokens[i + 1].slice(2), 'hex'),
+          len: opcodenum,
+          opcodenum: opcodenum
+        });
+        i = i + 2;
+      }
+      else {
+        throw new Error('Invalid script');
+      }
+    } else if (opcodenum === Opcode.map.OP_PUSHDATA1 || opcodenum === Opcode.map.OP_PUSHDATA2 || opcodenum === Opcode.map.OP_PUSHDATA4) {
+      this.chunks.push({
+        buf: new Buffer(tokens[i + 2].slice(2), 'hex'),
+        len: parseInt(tokens[i + 1]),
+        opcodenum: opcodenum
+      });
+      i = i + 3;
+    } else {
+      this.chunks.push(opcodenum);
+      i = i + 1;
+    }
+  }
+  return this;
+};
+
 Script.prototype.toString = function() {
   var str = "";
 
@@ -115,7 +153,8 @@ Script.prototype.toString = function() {
       str = str + Opcode(opcodenum).toString() + " ";
     } else {
       var opcodenum = chunk.opcodenum;
-      str = str + Opcode(opcodenum).toString() + " " ;
+      if (opcodenum === Opcode.map.OP_PUSHDATA1 || opcodenum === Opcode.map.OP_PUSHDATA2 || opcodenum === Opcode.map.OP_PUSHDATA4)
+        str = str + Opcode(opcodenum).toString() + " " ;
       str = str + chunk.len + " " ;
       str = str + "0x" + chunk.buf.toString('hex') + " ";
     }

test/script.js

@@ -151,6 +151,17 @@ describe('Script', function() {
 
   });
 
+  describe('#fromString', function() {
+
+    it('should parse these known scripts', function() {
+      Script().fromString('OP_0 OP_PUSHDATA4 3 0x010203 OP_0').toString().should.equal('OP_0 OP_PUSHDATA4 3 0x010203 OP_0');
+      Script().fromString('OP_0 OP_PUSHDATA2 3 0x010203 OP_0').toString().should.equal('OP_0 OP_PUSHDATA2 3 0x010203 OP_0');
+      Script().fromString('OP_0 OP_PUSHDATA1 3 0x010203 OP_0').toString().should.equal('OP_0 OP_PUSHDATA1 3 0x010203 OP_0');
+      Script().fromString('OP_0 3 0x010203 OP_0').toString().should.equal('OP_0 3 0x010203 OP_0');
+    });
+
+  });
+
   describe('#toString', function() {
 
     it('should output this buffer an OP code, data, and another OP code', function() {