Add a simple json module to Transcrypt

transcrypt/modules/json.py

@@ -0,0 +1,36 @@
+"""The simplest cases of Python's json implemented with JS JSON.
+
+https://docs.python.org/3/library/json.html
+
+https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON
+"""
+
+
+class JSONDecodeError(ValueError):
+    """Exception raised when a JSON document cannot be parsed."""
+
+    def __init__(self, msg: str, doc):  # noqa
+        # The interface is different in Python stdlib -- it has more variables,
+        # but we cannot do that because the SyntaxError object is different in
+        # each browser!
+        super().__init__(msg)
+        self.doc = doc  # the thing we tried to parse
+
+
+def loads(s: str):  # noqa
+    # The Python stdlib function has lots of kwargs; we don't.
+    # We catch the JS SyntaxError and raise the python JSONDecodeError
+    # in an attempt to resemble Python behavior.
+    # __pragma__ ('ecom') # ===================================================
+    # __pragma__ ("js", "{}", "try {return JSON.parse(s);}\ncatch (exc) {\nconsole.error(exc);\nvar py_exc = new JSONDecodeError(exc.message, s);\npy_exc.__cause__ = null;\nthrow py_exc;\n}")
+    # __pragma__ ('noecom') # =================================================
+
+
+def dumps(obj) -> str:  # noqa
+    # The Python stdlib function has lots of kwargs; we don't.
+    # JS: JSON.stringify(value, replacer, space)
+    result = JSON.stringify(obj, None, 2)
+    if result is js_undefined:
+        console.error("Not JSON serializable: ", obj)
+        raise ValueError("Object is not JSON serializable.")
+    return result