Comparing With === Instead of ==

Comparing With === Instead of ==

In this lesson, you ported the backup check’s one comparison and saw that JavaScript’s == converts types before comparing, as + and * do, where Python’s == doesn’t.

• Python’s == never treats text as equal to a number: the retry count as the text "5" and as the number 5 compare False. In the port, process.env holds the settings, and as in os.environ, every value that’s set is text. The retry count goes through Number(), its default for an unset variable left for later.
• The flag’s line, ported with ==, works on the new server, because both sides of its comparison are text. When both sides are text, == compares the way Python’s does. JavaScript’s true and false are lowercase, where Python writes a capital.
• When the types don’t match, == converts first, so "5" == 5 is true. As a test of how far that goes, "0" == false is true too: == turns both sides into numbers, false into 0 and the text "0" into 0. Python also treats False as zero, but it never turns text into a number.
• "0" == false is a comparison, not a truth test: in an if, the text "0" still counts as true. Empty text turns into zero as well, as it does with Number(), so 0 == "" is true. Python says False to "5" == 5, "0" == False, and 0 == "" alike.
• With ==, text passes for a number: a retry count left as text would still equal 5, so the comparison hides the missing conversion.
• ===, the operator you’ve used to check for null and undefined, never converts. For text, numbers, and booleans, it’s true only when both sides have the same type and the same value, so text never equals a number, as in Python. "5" === 5, "0" === false, and 0 === "" are all false. == is called loose equality, and === strict equality. The full rules for loose equality come later.
• The flag’s line worked with ==, but === gives Python’s answers here, and you don’t have to check both sides’ types to trust it, so it’s what JavaScript developers write by default. To compare a setting as a number, convert it with Number() first: Number("5") === 5 is true.
• Not-equals comes in the same two kinds: != converts, so "5" != 5 is false, and !== doesn’t, so "5" !== 5 is true, as Python’s "5" != 5 is True.
• The rule: write === and !== everywhere, and convert text with Number() before you compare it as a number. Loose equality’s one use on purpose is x == null, which catches null and undefined together.

Here’s the port’s flag and retry count, written the JavaScript way:

const dryRun = process.env.DRY_RUN === "1";
const retries = Number(process.env.BACKUP_RETRIES);

console.log(`Dry run: ${dryRun}`);
console.log(`Up to ${retries + 1} attempts`);