Compare values using JavaScript semantics in Python. Not sure if I got everything right. This is more of a demonstration that JavaScript equality semantics are crazy.

js_equals.py

# Copyright 2021 Mathias Panzenböck
#
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in all
# copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
# SOFTWARE.

# dict is a stand-in for all plain JavaScript objects in this.
def js_equals(a, b) -> bool:
	if type(a) is type(b):
		# To be more strict it should be `a is b` if they're list or dict
		# (i.e. objects in JavaScript).
		return a == b

	if isinstance(a, (int, float)):
		if isinstance(b, (int, float)):
			return a == b
		return a == to_float(b)

	if isinstance(b, (int, float)):
		return to_float(a) == b

	if a is None or b is None:
		return False

	if isinstance(a, str):
		if isinstance(b, bool):
			return to_float(a) == to_float(b)

		if isinstance(b, (list, dict)):
			return a == to_string(b)

		raise TypeError

	if isinstance(a, bool):
		return to_float(a) == to_float(b)

	if isinstance(a, (list, dict)):
		if isinstance(b, (list, dict)):
			return False

		if isinstance(b, str):
			return to_string(a) == b

		if isinstance(b, bool):
			return to_float(a) == to_float(b)

		raise TypeError

	raise TypeError

def to_float(a) -> float:
	if a is None:
		return 0.0

	if isinstance(a, list):
		if not a:
			return 0.0
		elif len(a) > 1:
			return float('nan')
		else:
			return to_float(a[0])

	if isinstance(a, dict):
		return float('nan')

	try:
		# XXX: This accepts a little bit too much. I.e. it will allow
		#      'inf', '+inf', and '-inf', where JavaScript only allows
		#      'Infinity', '+Infinity', and '-Infinity' (which this
		#      also allows).
		return float(a)
	except ValueError:
		return float('nan')

def to_string(a) -> str:
	if isinstance(a, str):
		return a

	if isinstance(a, (int, float)):
		return str(a)

	if a is None:
		return 'null'

	if a is True:
		return 'true'

	if a is False:
		return 'false'

	if isinstance(a, list):
		return ','.join(to_string(b) for b in a)

	if isinstance(a, dict):
		return '[object Object]'

	# Note that this calls a.toString() in JavaScript.
	# Meaning it returns something different for any object in
	# JavaScript. E.g. for Date it returns something like:
	# "Wed Sep 08 2021 05:57:22 GMT+0200 (Central European Summer Time)"
	# Meanig you can compare a date with a string formated like
	# that and if the date would be formatting to the string it
	# yields true.
	raise TypeError