Chapter 1

Here are the solutions to the Exercises, for the Chapter 1, JavaScript Gotchas chapter.

	//That's one strange comparison, but given the choices, choose ===
	"2.0" / 2 * "2.0" === 2 / 2 * 2;

	console.log(canVote(12)); //no, can't vote
	console.log(canVote("12")); //no, can't vote
	console.log(canVote(17)); //no, can't vote
	console.log(canVote('@18')); //no, can't vote
	console.log(canVote(18)); //yay, start voting
	console.log(canVote(28)); //please vote

	//The code as given in the exercise will not terminate.

	//Here's the fix: use option strict and declare i before use in the two loops
	'use strict';

	const isPrime = function(n) {
	for(let i = 2; i <= Math.sqrt(n); i++) {//or < n instead of <= Math.sqrt(n)
	if(n % i === 0) return false;
	}

	return n > 1;
	};

	const sumOfPrimes = function(n) {
	let sum = 0;
	for(let i = 1; i <= n; i++) {
	if(isPrime(i)) sum += i;
	}

	return sum;
	};

	console.log(sumOfPrimes(10));

ESLint reported the following errors for the given code:

	1:1 error Use the global form of 'use strict' strict
	1:1 error Unexpected var, use let or const instead no-var
	2:3 error Unexpected var, use let or const instead no-var
	4:7 error 'index' is not defined no-undef
	4:18 error 'index' is not defined no-undef
	4:35 error 'index' is not defined no-undef
	5:17 error 'index' is not defined no-undef
	5:23 error Expected '===' and instead saw '==' eqeqeq
	6:23 error 'index' is not defined no-undef
	11:5 error Expected '===' and instead saw '==' eqeqeq
	14:5 error 'i' is not defined no-undef
	14:12 error 'i' is not defined no-undef
	14:21 error 'i' is not defined no-undef
	15:23 error 'i' is not defined no-undef
	15:53 error 'i' is not defined no-undef

	✖ 15 problems (15 errors, 0 warnings)
	2 errors, 0 warnings potentially fixable with the `--fix` option.

Here’s the code after removing the errors—using const where possible and let instead of var:

	'use strict';

	const isPerfect = function(number) {
	let sumOfFactors = 0;

	for(let index = 1; index <= number; index++) {
	if(number % index === 0) {
	sumOfFactors += index;
	}
	}

	return sumOfFactors === number * 2;
	};

	for(let i = 1; i <= 10; i++) {
	console.log('is ' + i + ' perfect?: ' + isPerfect(i));
	}

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Table of Contents for Chapter 1