This course shows you how to catch, throw, and tell apart JavaScript errors, and find what went
wrong. Python’s try looks the same in JavaScript, but JavaScript throws less often on bad
data, so code that waits for an error to reject bad data lets it slip through, and its catch
takes every error, not only the ones you meant to handle. This is the last course on the beginner
path.
Your project is to port a food bank’s donation import, the Python script its volunteer treasurer
runs, to JavaScript. Here’s a first taste. Her script, donations.py, totals the good rows of
October’s export. Here are the parts that check each amount:
Language: Python
def parse_amount(text):
amount = float(text)
if amount <= 0:
raise ValueError(f"amount must be positive, got {amount}")
return amount
def main():
# ... reads the rows of the export ...
total = 0
rejected = []
for line, row in enumerate(rows[1:], start=2):
date, donor, amount_text = row
try:
amount = parse_amount(amount_text)
except ValueError as err:
rejected.append((line, donor, str(err)))
else:
total += amount
# ... prints the report ...
Run as python donations.py october.csv, it rejects four rows, each with a reason:
Language: Program Output
6 rows, 4 rejected, total £125.00
line 3 (D-102): could not convert string to float: 'n/a'
line 4 (D-117): could not convert string to float: ''
line 5 (D-104): could not convert string to float: '1,250.00'
line 6 (D-105): amount must be positive, got -40.0
