Pairing Up Arrays Without zip()

Pairing Up Arrays Without zip()

In this lesson, you paired the night-bus report’s timetable with the trip feed’s actual departure times, in JavaScript.

• JavaScript has no zip(). To pair two arrays, count through the positions with a classic for loop, and read both arrays at each position with square brackets.
• Python’s zip() stops at the end of the shorter list. A counting loop stops only where its condition says. Loop up to the longer array’s .length, and the last passes read positions that the shorter array doesn’t have.
• Reading a position that an array doesn’t have gives undefined, JavaScript’s empty value, and no error. Python raises an IndexError there. Inside a template literal, undefined turns into the text undefined.
• Python’s zip() stops silently, which can hide missing data in Python too. When the lists must be the same length, zip(..., strict=True) (Python 3.10 and later) raises a ValueError instead.
• To stop where zip() stops, loop up to the smaller of the two lengths. Python’s min() is a built-in function. JavaScript has no global min(): it keeps min(), with its other math functions, on the built-in Math object, much like Python’s math module, which has no min() of its own. Writing the stop on its own line makes your choice visible to the next reader.
• Math.min() takes the numbers as separate arguments. Hand it an array, and it doesn’t throw an error: it returns NaN, JavaScript’s “not a number” value.

The finished pairing loop:

const scheduled = ["23:10", "23:30", "23:50"];
const actual = ["23:14", "23:30", "00:02", "00:10"];
const pairCount = Math.min(scheduled.length, actual.length);
for (let i = 0; i < pairCount; i++) {
  console.log(`${scheduled[i]} left at ${actual[i]}`);
}