Numbers, Math & Date

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Number Methods

const n = 123.456;

n.toFixed(2);          // "123.46" (string, rounded)
n.toPrecision(5);      // "123.46" (5 significant digits)
n.toString();          // "123.456"
n.toString(16);        // hex string
n.toString(2);         // binary string

// Number static methods
Number.isInteger(5);       // true
Number.isInteger(5.5);     // false
Number.isFinite(Infinity); // false
Number.isFinite(5);        // true
Number.isNaN(NaN);         // true
Number.isNaN("abc");       // false (strict!)
Number.parseInt("42.9");   // 42
Number.parseFloat("42.9"); // 42.9

// Safe integer range
Number.MAX_SAFE_INTEGER; // 9007199254740991 (2^53 - 1)
Number.MIN_SAFE_INTEGER; // -9007199254740991
Number.isSafeInteger(9007199254740991);  // true
Number.isSafeInteger(9007199254740992);  // false

// Special values
Number.MAX_VALUE;
Number.MIN_VALUE;
Number.POSITIVE_INFINITY;
Number.NEGATIVE_INFINITY;
Number.EPSILON; // smallest float difference

// Floating point gotcha!
0.1 + 0.2 === 0.3;    // false (floating point precision!)
(0.1 + 0.2).toFixed(1) === "0.3"; // true (workaround)
Math.abs(0.1 + 0.2 - 0.3) < Number.EPSILON; // true (proper comparison)

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Math Object

Math.PI;          // 3.141592653589793
Math.E;           // 2.718281828459045
Math.SQRT2;       // 1.414...

// Rounding
Math.round(4.5);  // 5 (rounds .5 up)
Math.round(4.4);  // 4
Math.floor(4.9);  // 4 (always down)
Math.ceil(4.1);   // 5 (always up)
Math.trunc(4.9);  // 4 (remove decimal, toward zero)
Math.trunc(-4.9); // -4

// Min / Max
Math.max(1, 5, 3);         // 5
Math.min(1, 5, 3);         // 1
Math.max(...[1, 5, 3]);    // 5 (spread array)

// Powers and roots
Math.pow(2, 10);   // 1024 (same as 2**10)
Math.sqrt(16);     // 4
Math.cbrt(27);     // 3 (cube root)
Math.hypot(3, 4);  // 5 (Pythagorean theorem)

// Logarithms
Math.log(Math.E);  // 1 (natural log)
Math.log2(8);      // 3 (base 2)
Math.log10(100);   // 2 (base 10)

// Trig
Math.sin(Math.PI / 2); // 1
Math.cos(0);           // 1

// Random
Math.random();                       // 0 <= x < 1
Math.floor(Math.random() * 6) + 1;  // random int 1-6 (dice)

// Random integer between min and max (inclusive)
const randInt = (min, max) => Math.floor(Math.random() * (max - min + 1)) + min;

Math.abs(-5);      // 5 (absolute value)
Math.sign(-3);     // -1 (negative)
Math.sign(0);      // 0
Math.sign(3);      // 1 (positive)

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Date Object

// Creating dates
const now = new Date();                    // current date/time
const d1 = new Date(2024, 0, 15);          // Jan 15, 2024 (months are 0-indexed!)
const d2 = new Date("2024-03-25");         // from ISO string
const d3 = new Date(1711324800000);        // from Unix timestamp (ms)

// Getting parts
const d = new Date();
d.getFullYear();     // 4-digit year
d.getMonth();        // 0-11 (0 = January!)
d.getDate();         // 1-31 (day of month)
d.getDay();          // 0-6 (0 = Sunday)
d.getHours();        // 0-23
d.getMinutes();      // 0-59
d.getSeconds();      // 0-59
d.getTime();         // Unix timestamp in ms

// Setting parts
d.setFullYear(2025);
d.setMonth(11);      // December
d.setDate(31);

// Formatting
d.toISOString();              // "2024-03-25T10:30:00.000Z"
d.toLocaleDateString();       // "3/25/2024"
d.toLocaleString("en-IN");    // Indian locale format

// Better formatting with Intl
new Intl.DateTimeFormat("en-US", {
  weekday: "long",
  year: "numeric",
  month: "long",
  day: "numeric"
}).format(new Date()); // "Wednesday, March 25, 2026"

// Date arithmetic
const tomorrow = new Date(Date.now() + 86400000);
const diffMs = new Date("2025-01-01") - new Date();
const diffDays = Math.floor(diffMs / 86400000);

// Performance timing
const start = Date.now();
// ... some code ...
const elapsed = Date.now() - start; // ms elapsed

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MCQ — Numbers, Math & Date

Q1: What is 0.1 + 0.2 === 0.3 in JavaScript?

A) true B) false ✅ C) Depends on the JS engine D) NaN

Answer: B — Floating point precision issue. 0.1 + 0.2 = 0.30000000000000004.

Q2: What does new Date().getMonth() return for January?

A) 1 B) 0 ✅ C) "January" D) "Jan"

Answer: B — Months are 0-indexed: 0 = January, 11 = December.

Q3: What does Math.trunc(-4.7) return?

A) -5 B) -4 ✅ C) 4 D) 5

Answer: B — trunc removes the decimal toward zero. -4.7 becomes -4.

Q4: What is Number.MAX_SAFE_INTEGER?

A) The maximum number JS can represent B) 2^53 - 1 = 9007199254740991 ✅ C) 2^32 - 1 D) Infinity

Answer: B — Integers above this can lose precision. Use BigInt for larger values.

Q5: How do you generate a random integer from 1 to 10?

A) Math.random() * 10 B) Math.round(Math.random() * 10) C) Math.floor(Math.random() * 10) + 1 ✅ D) parseInt(Math.random() * 10)

Answer: C — Math.floor(Math.random() * 10) gives 0-9, +1 shifts to 1-10.