JavaScript Numbers, Math, and BigInt

// Decimal integers
const dec = 42;
const negative = -17;
const zero = 0;

// Decimal floats
const pi = 3.14159;
const small = 0.0001;
const leading = .5; // 0.5 (avoid - use 0.5)
const trailing = 5.; // 5 (avoid - use 5.0 or 5)

// Scientific notation
const million = 1e6; // 1000000
const billion = 1e9; // 1000000000
const tiny = 5e-3; // 0.005
const planck = 6.62607015e-34;

// Binary (base 2)
const binary = 0b1010; // 10
const flags = 0b11111111; // 255
const mask = 0b1100; // 12

// Octal (base 8)
const octal = 0o17; // 15
const permissions = 0o755; // 493 (rwxr-xr-x)

// Hexadecimal (base 16)
const hex = 0xFF; // 255
const color = 0xFF5733; // 16734003
const byte = 0xAB; // 171

// Mixed case OK
const HEX = 0XFF; // 255
const BIN = 0B1010; // 10

// Numeric separators (readability)
const oneMillion = 1_000_000;
const billion = 1_000_000_000;
const hexColor = 0xFF_55_33;
const binary8bit = 0b1111_0000;
const creditCard = 1234_5678_9012_3456;

// Separators anywhere except start/end
const amount = 123_456.789_012;

// Special values
const inf = Infinity;
const negInf = -Infinity;
const notANumber = NaN;

1 / 0; // Infinity
-1 / 0; // -Infinity
0 / 0; // NaN
Math.sqrt(-1); // NaN

// NaN is unique
NaN === NaN; // false ❌
isNaN(NaN); // true ✓
Number.isNaN(NaN); // true ✓ (preferred)

// Signed zeros
+0 === -0; // true
Object.is(+0, -0); // false (can distinguish)

1 / +0; // Infinity
1 / -0; // -Infinity

// Type checking
typeof 42; // "number"
typeof 3.14; // "number"
typeof NaN; // "number" (yes, really!)
typeof Infinity; // "number"

// Number range
Number.MAX_VALUE; // ~1.79e308
Number.MIN_VALUE; // ~5e-324 (smallest positive)
Number.MAX_SAFE_INTEGER; // 2^53 - 1 (9007199254740991)
Number.MIN_SAFE_INTEGER; // -(2^53 - 1)

// Type checking methods
Number.isFinite(42); // true
Number.isFinite(Infinity); // false
Number.isFinite(NaN); // false
Number.isFinite('42'); // false (no coercion!)

// Compare: global isFinite() coerces
isFinite('42'); // true (coerces to 42)
Number.isFinite('42'); // false (no coercion)

Number.isInteger(42); // true
Number.isInteger(42.0); // true (same as 42)
Number.isInteger(42.5); // false
Number.isInteger('42'); // false

Number.isNaN(NaN); // true
Number.isNaN(42); // false
Number.isNaN('hello'); // false (no coercion!)

// Compare: global isNaN() coerces
isNaN('hello'); // true (coerces to NaN)
Number.isNaN('hello'); // false (no coercion)

Number.isSafeInteger(42); // true
Number.isSafeInteger(9007199254740991); // true (MAX_SAFE_INTEGER)
Number.isSafeInteger(9007199254740992); // false (too large)
Number.isSafeInteger(42.5); // false (not integer)

// Formatting methods
const num = 123.456;

num.toFixed(2); // "123.46" (rounds)
num.toFixed(0); // "123"
num.toFixed(5); // "123.45600"

num.toExponential(2); // "1.23e+2"
(1234.5).toExponential(); // "1.2345e+3"

num.toPrecision(4); // "123.5"
num.toPrecision(2); // "1.2e+2" (switches to exponential)
num.toPrecision(10); // "123.4560000"

// Base conversion
(255).toString(); // "255"
(255).toString(16); // "ff" (hex)
(255).toString(2); // "11111111" (binary)
(255).toString(8); // "377" (octal)
(255).toString(36); // "73" (max base)

// Locale formatting
const price = 1234.56;
price.toLocaleString('en-US', {
    style: 'currency',
    currency: 'USD'
}); // "$1,234.56"

price.toLocaleString('de-DE', {
    style: 'currency',
    currency: 'EUR'
}); // "1.234,56 €"

const percent = 0.755;
percent.toLocaleString('en-US', {
    style: 'percent',
    minimumFractionDigits: 1
}); // "75.5%"

// Constants
Number.EPSILON; // 2.220446049250313e-16
Number.MAX_VALUE; // 1.7976931348623157e+308
Number.MIN_VALUE; // 5e-324
Number.MAX_SAFE_INTEGER; // 9007199254740991
Number.MIN_SAFE_INTEGER; // -9007199254740991

// Safe integer range check
function isSafeArithmetic(a, b) {
    const result = a + b;
    return Number.isSafeInteger(a) &&
           Number.isSafeInteger(b) &&
           Number.isSafeInteger(result);
}

// Floating point comparison with EPSILON
function almostEqual(a, b) {
    return Math.abs(a - b) < Number.EPSILON;
}

almostEqual(0.1 + 0.2, 0.3); // true
0.1 + 0.2 === 0.3; // false ❌

// Format large numbers
const large = 1234567890;
large.toLocaleString('en-US'); // "1,234,567,890"

// Scientific notation
(0.0000001).toExponential(); // "1e-7"
(10000000).toExponential(); // "1e+7"

// Precision control
const value = 123.456789;
value.toFixed(2); // "123.46"
value.toPrecision(5); // "123.46"
parseFloat(value.toFixed(2)); // 123.46 (back to number)

// Rounding
Math.round(4.5); // 5
Math.round(4.4); // 4
Math.round(-4.5); // -4 (rounds to nearest even)

Math.ceil(4.1); // 5 (always up)
Math.floor(4.9); // 4 (always down)
Math.trunc(4.9); // 4 (remove decimal)

// Difference: floor vs trunc with negatives
Math.floor(-4.1); // -5 (down = more negative)
Math.trunc(-4.1); // -4 (just removes decimal)

// Absolute value and sign
Math.abs(-5); // 5
Math.abs(5); // 5

Math.sign(-5); // -1
Math.sign(0); // 0
Math.sign(5); // 1

// Min/Max
Math.min(5, 2, 8, 1); // 1
Math.max(5, 2, 8, 1); // 8

// With arrays (spread)
const nums = [5, 2, 8, 1];
Math.min(...nums); // 1
Math.max(...nums); // 8

// Power and roots
Math.pow(2, 3); // 8
2 ** 3; // 8 (exponentiation operator - preferred)

Math.sqrt(16); // 4
Math.sqrt(2); // 1.4142135623730951
Math.cbrt(27); // 3
Math.cbrt(8); // 2

// Logarithms
Math.log(Math.E); // 1 (natural log)
Math.log10(100); // 2
Math.log2(8); // 3

// Exponential
Math.exp(1); // 2.718281828459045 (e^1)
Math.exp(2); // 7.389... (e^2)

// Random numbers
Math.random(); // 0 <= x < 1

// Random integer in range [min, max]
function randomInt(min, max) {
    return Math.floor(Math.random() * (max - min + 1)) + min;
}
randomInt(1, 6); // dice roll (1-6)

// Random from array
function randomItem(arr) {
    return arr[Math.floor(Math.random() * arr.length)];
}

// Trigonometry (radians!)
Math.sin(Math.PI / 2); // 1
Math.cos(0); // 1
Math.tan(Math.PI / 4); // ~1

// Degrees to radians
function toRadians(degrees) {
    return degrees * Math.PI / 180;
}

// Radians to degrees
function toDegrees(radians) {
    return radians * 180 / Math.PI;
}

Math.sin(toRadians(30)); // 0.5

// atan2 - angle from origin to point
Math.atan2(1, 1); // π/4 (45 degrees)
Math.atan2(1, 0); // π/2 (90 degrees)

// Hypotenuse (Pythagorean)
Math.hypot(3, 4); // 5 (3² + 4² = 5²)
Math.hypot(1, 1); // √2 (1.414...)

// Distance between 2D points
function distance(x1, y1, x2, y2) {
    return Math.hypot(x2 - x1, y2 - y1);
}

// Constants
Math.PI; // 3.141592653589793
Math.E; // 2.718281828459045

// Circle calculations
const radius = 5;
const circumference = 2 * Math.PI * radius; // 31.4...
const area = Math.PI * radius ** 2; // 78.5...

// Practical uses
// 1. Clamp value to range
function clamp(value, min, max) {
    return Math.min(Math.max(value, min), max);
}

// 2. Linear interpolation
function lerp(start, end, t) {
    return start + (end - start) * t;
}

// 3. Map value from one range to another
function map(value, inMin, inMax, outMin, outMax) {
    return (value - inMin) * (outMax - outMin) / (inMax - inMin) + outMin;
}

// 4. Round to decimal places
function roundTo(num, places) {
    const factor = 10 ** places;
    return Math.round(num * factor) / factor;
}
roundTo(3.14159, 2); // 3.14

// Classic floating point problem
0.1 + 0.2; // 0.30000000000000004 ❌
0.1 + 0.2 === 0.3; // false

// Epsilon comparison for floats
function almostEqual(a, b, epsilon = Number.EPSILON) {
    return Math.abs(a - b) < epsilon;
}

almostEqual(0.1 + 0.2, 0.3); // true ✓

// For larger numbers, scale epsilon
function almostEqualScaled(a, b) {
    const epsilon = Math.max(Math.abs(a), Math.abs(b)) * Number.EPSILON;
    return Math.abs(a - b) <= epsilon;
}

// Round to fixed decimals
function roundTo(num, decimals) {
    const factor = 10 ** decimals;
    return Math.round(num * factor) / factor;
}

roundTo(0.1 + 0.2, 1); // 0.3 ✓
roundTo(1.005, 2); // 1.01 (beware banker's rounding)

// Integer math for currency (cents)
// ❌ Don't do this:
const price = 0.1 + 0.2; // 0.30000000000000004

// ✓ Do this:
const priceInCents = 10 + 20; // 30
const price = priceInCents / 100; // 0.3

// Financial calculations
function addCurrency(a, b) {
    return (a * 100 + b * 100) / 100;
}
addCurrency(0.1, 0.2); // 0.3 ✓

// Large integer precision loss
const maxSafe = Number.MAX_SAFE_INTEGER; // 9007199254740991

maxSafe + 1; // 9007199254740992 ✓
maxSafe + 2; // 9007199254740992 ❌ (lost precision!)

// Check safe integer range
Number.isSafeInteger(maxSafe); // true
Number.isSafeInteger(maxSafe + 1); // true
Number.isSafeInteger(maxSafe + 2); // false

// Division by zero
1 / 0; // Infinity (not error!)
-1 / 0; // -Infinity
0 / 0; // NaN

// Check for valid result
function safeDivide(a, b) {
    if (b === 0) return null;
    return a / b;
}

// NaN propagation
const result = NaN + 5; // NaN
Math.sqrt(-1) * 2; // NaN

// Always check NaN
function safeCalculation(a, b) {
    const result = a / b;
    if (Number.isNaN(result)) {
        throw new Error('Invalid calculation');
    }
    return result;
}

// Rounding modes
Math.round(2.5); // 3
Math.round(-2.5); // -2 (rounds towards zero for negatives)

Math.floor(2.9); // 2
Math.floor(-2.1); // -3 (towards negative infinity)

Math.ceil(2.1); // 3
Math.ceil(-2.9); // -2 (towards positive infinity)

Math.trunc(2.9); // 2
Math.trunc(-2.9); // -2 (just removes decimal)

// Banker's rounding (round half to even)
function bankersRound(num, decimals = 0) {
    const factor = 10 ** decimals;
    const n = num * factor;
    const floor = Math.floor(n);
    const diff = n - floor;
    
    if (diff === 0.5) {
        return floor % 2 === 0 ? floor / factor : Math.ceil(n) / factor;
    }
    return Math.round(n) / factor;
}

// Comparing with tolerance
function withinTolerance(a, b, tolerance = 0.001) {
    return Math.abs(a - b) <= tolerance;
}

withinTolerance(0.1 + 0.2, 0.3, 0.001); // true

// Use decimal libraries for precision
// npm install decimal.js
// const Decimal = require('decimal.js');
// new Decimal(0.1).plus(0.2).equals(0.3); // true

// Creation
const big1 = 9007199254740993n; // literal with n suffix
const big2 = BigInt(9007199254740993); // constructor
const big3 = BigInt("9007199254740993"); // from string (for very large)

// Cannot mix BigInt and Number
10n + 20; // ❌ TypeError: Cannot mix BigInt and other types
10n + 20n; // ✓ 30n

// Convert between types
const num = 42;
const big = BigInt(num); // Number to BigInt
const backToNum = Number(big); // BigInt to Number (may lose precision!)

// Arithmetic operations
100n + 50n; // 150n
100n - 50n; // 50n
10n * 20n; // 200n

// Division truncates (integer division)
10n / 3n; // 3n (not 3.333...)
-10n / 3n; // -3n (rounds towards zero)

10n % 3n; // 1n (remainder)

// Exponentiation
2n ** 100n; // huge number
2n ** -1n; // ❌ RangeError: exponent must be non-negative

// Comparison
10n < 20n; // true
10n === 10n; // true
10n === 10; // false (strict equality - different types)
10n == 10; // true (loose equality - coerces)

// Mixed comparisons (non-equality)
10n < 20; // true ✓
10n > 5; // true ✓
20n <= 20; // true ✓

// Bitwise operations
const a = 5n; // 0101
const b = 3n; // 0011

a & b; // 1n (0001)
a | b; // 7n (0111)
a ^ b; // 6n (0110)
~a; // -6n (bitwise NOT)

5n << 2n; // 20n (shift left)
20n >> 2n; // 5n (shift right)

// No unsigned right shift (>>>) for BigInt

// Large factorials (no overflow!)
function factorial(n) {
    let result = 1n;
    for (let i = 2n; i <= n; i++) {
        result *= i;
    }
    return result;
}

factorial(100n); // huge number (no precision loss!)

// Compare with regular number (loses precision)
function factorialNumber(n) {
    let result = 1;
    for (let i = 2; i <= n; i++) {
        result *= i;
    }
    return result;
}
factorialNumber(100); // Infinity (overflow!)

// Large integer operations
const maxSafe = BigInt(Number.MAX_SAFE_INTEGER);
maxSafe + 1n; // works correctly!
maxSafe + 2n; // still correct!

// Crypto/hashing with BigInt
const large = 2n ** 256n; // 256-bit number

// No fractional BigInt
const frac = 1.5n; // ❌ SyntaxError
const fromFloat = BigInt(1.5); // ❌ RangeError

// Must be integer
const safe = BigInt(Math.floor(1.5)); // ✓ 1n

// Type checking
typeof 10n; // "bigint"
10n instanceof BigInt; // ❌ false (primitives not instances)

// Conversion gotchas
Number(2n ** 100n); // Infinity (too large for Number!)

// Safe conversion check
function safeToNumber(bigint) {
    const num = Number(bigint);
    if (!Number.isSafeInteger(num)) {
        throw new Error('BigInt too large for safe Number conversion');
    }
    return num;
}

// JSON doesn't support BigInt
JSON.stringify({value: 10n}); // ❌ TypeError

// Custom JSON serialization
JSON.stringify({value: 10n}, (key, value) =>
    typeof value === 'bigint' ? value.toString() : value
); // '{"value":"10"}'

// Math methods don't work with BigInt
Math.max(10n, 20n); // ❌ TypeError
Math.sqrt(100n); // ❌ TypeError

// Must use BigInt operations
function maxBigInt(...args) {
    return args.reduce((max, val) => val > max ? val : max);
}
maxBigInt(10n, 50n, 30n); // 50n

// Practical: microsecond timestamps
const timestamp = BigInt(Date.now()) * 1000n; // microseconds

// Practical: precise money calculations
const cents = 12345n; // $123.45
const dollars = Number(cents) / 100; // 123.45

// parseInt - parses until invalid character
parseInt('123'); // 123
parseInt('123.45'); // 123 (stops at decimal)
parseInt('123px'); // 123 (stops at 'p')
parseInt('abc'); // NaN (no valid digits)
parseInt('  42'); // 42 (trims whitespace)

// Always specify radix!
parseInt('08'); // 8 (may be octal in old browsers without radix!)
parseInt('08', 10); // 8 ✓ (always use radix)

// Different bases
parseInt('FF', 16); // 255 (hexadecimal)
parseInt('1010', 2); // 10 (binary)
parseInt('77', 8); // 63 (octal)
parseInt('Z', 36); // 35 (max base)

// Radix validation
parseInt('123', 10); // 123
parseInt('123', 2); // 1 (stops at '2', invalid for binary)

// parseFloat - decimal parsing
parseFloat('123.45'); // 123.45
parseFloat('123.45.67'); // 123.45 (stops at second '.')
parseFloat('123.45px'); // 123.45 (stops at 'p')
parseFloat('.5'); // 0.5
parseFloat('5.'); // 5

// Scientific notation
parseFloat('1.23e10'); // 12300000000
parseFloat('1e-5'); // 0.00001

// Number() - strict conversion
Number('123'); // 123
Number('123.45'); // 123.45
Number('123px'); // NaN ❌ (entire string must be valid)
Number('  42  '); // 42 (trims whitespace)
Number(''); // 0 (empty string is 0!)
Number('   '); // 0 (whitespace only is 0)

// Unary plus (shorthand)
+'123'; // 123
+'123.45'; // 123.45
+'123px'; // NaN

// Comparison: parseInt vs parseFloat vs Number
const str = '123.45px';
parseInt(str); // 123 (stops at decimal)
parseFloat(str); // 123.45 (stops at 'p')
Number(str); // NaN (invalid)

// Type coercion gotchas
Number(true); // 1
Number(false); // 0
Number(null); // 0
Number(undefined); // NaN
Number([]); // 0 (empty array)
Number([5]); // 5 (single element)
Number([1, 2]); // NaN (multiple elements)

// Validation: isNaN vs Number.isNaN
isNaN('hello'); // true (coerces 'hello' to NaN)
Number.isNaN('hello'); // false (string is not NaN)
Number.isNaN(NaN); // true ✓

isNaN(undefined); // true (coerces to NaN)
Number.isNaN(undefined); // false (undefined is not NaN)

// Rule: Use Number.isNaN() for strict checking
Number.isNaN(0 / 0); // true
Number.isNaN(parseFloat('abc')); // true

// Validation: isFinite vs Number.isFinite
isFinite('123'); // true (coerces to 123)
Number.isFinite('123'); // false (string is not finite number)

isFinite(Infinity); // false
Number.isFinite(Infinity); // false

isFinite(NaN); // false
Number.isFinite(NaN); // false

// Rule: Use Number.isFinite() for strict checking

// Integer validation
Number.isInteger(42); // true
Number.isInteger(42.0); // true (same as 42)
Number.isInteger(42.5); // false
Number.isInteger('42'); // false (no coercion)

// Safe integer validation
Number.isSafeInteger(42); // true
Number.isSafeInteger(Number.MAX_SAFE_INTEGER); // true
Number.isSafeInteger(Number.MAX_SAFE_INTEGER + 1); // false
Number.isSafeInteger(42.0); // true

// Practical validation functions
function isValidNumber(value) {
    return typeof value === 'number' &&
           Number.isFinite(value) &&
           !Number.isNaN(value);
}

function parseOrDefault(str, defaultValue = 0) {
    const num = parseFloat(str);
    return Number.isNaN(num) ? defaultValue : num;
}

function strictParse(str) {
    const num = Number(str);
    if (Number.isNaN(num)) {
        throw new Error(`Invalid number: ${str}`);
    }
    return num;
}

// Safe parsing
function safeParse(str) {
    const trimmed = str.trim();
    if (trimmed === '') return null;
    
    const num = Number(trimmed);
    return Number.isNaN(num) ? null : num;
}

safeParse('123'); // 123
safeParse('abc'); // null
safeParse(''); // null

// Parsing with validation
function parsePositiveInt(str) {
    const num = parseInt(str, 10);
    if (Number.isNaN(num) || num <= 0 || !Number.isInteger(num)) {
        return null;
    }
    return num;
}

// Currency parsing
function parseCurrency(str) {
    // Remove currency symbols and commas
    const cleaned = str.replace(/[$,]/g, '');
    const num = parseFloat(cleaned);
    return Number.isNaN(num) ? null : num;
}

parseCurrency('$1,234.56'); // 1234.56
parseCurrency('€1.234,56'); // requires more complex parsing

// Input validation
function validateInput(input) {
    // Check if empty
    if (!input || input.trim() === '') {
        return {valid: false, error: 'Input required'};
    }
    
    // Try to parse
    const num = Number(input);
    
    // Check if valid number
    if (Number.isNaN(num)) {
        return {valid: false, error: 'Not a valid number'};
    }
    
    // Check if finite
    if (!Number.isFinite(num)) {
        return {valid: false, error: 'Must be finite'};
    }
    
    return {valid: true, value: num};
}