JavaScript Numbers Cheatsheet

Number constants

Number methods

Parsing numbers

Number.parseInt()

Parses a string and returns an integer. Always specify the base to avoid unexpected results.

Number.parseInt("42", 10); // 42
Number.parseInt("ff", 16); // 255
Number.parseInt("10px"); // 10

Number.parseFloat()

Parses a string and returns a floating-point number.

Number.parseFloat("3.14"); // 3.14
Number.parseFloat("10.5px"); // 10.5

Number()

Converts a value to a number. Whitespace is ignored.

Number("  100  "); // 100
Number("3.14"); // 3.14
Number(""); // 0
Number("hello"); // NaN

+ (unary plus)

The unary plus operator converts a string to a number. Prefer Number() for clarity.

+"99"; // 99
+"3.14"; // 3.14
+true; // 1

Formatting numbers

toFixed()

Returns a string with a fixed number of decimal places.

(1.2345).toFixed(2); // "1.23"
(10).toFixed(4); // "10.0000"

toPrecision()

Returns a string with a specified total number of significant digits.

(1.2345).toPrecision(3); // "1.23"
(1234).toPrecision(2); // "1.2e+3"

toString()

Returns a string representation in the given base.

(255).toString(16); // "ff"
(8).toString(2); // "1000"

toLocaleString()

Returns a language-sensitive formatted string.

(1234567).toLocaleString("en-US"); // "1,234,567"
(1234.5).toLocaleString("de-DE"); // "1.234,5"

toExponential()

Returns a string in exponential notation.

(12345).toExponential(2); // "1.23e+4"

Math helpers

Math.round()

Rounds to the nearest integer.

Math.round(4.4); // 4
Math.round(4.5); // 5

Math.floor()

Rounds down to the nearest integer.

Math.floor(4.9); // 4
Math.floor(-4.1); // -5

Math.ceil()

Rounds up to the nearest integer.

Math.ceil(4.1); // 5
Math.ceil(-4.9); // -4

Math.trunc()

Removes the decimal part.

Math.trunc(4.9); // 4
Math.trunc(-4.9); // -4

Math.abs()

Returns the absolute value.

Math.abs(-5); // 5

Math.max() / Math.min()

Return the largest or smallest of the given values.

Math.max(1, 5, 3); // 5
Math.min(1, 5, 3); // 1

Math.random()

Returns a random number from 0 (inclusive) to 1 (exclusive).

Math.random(); // e.g., 0.374829

Math.pow() / Math.sqrt()

Exponentiation and square root.

Math.pow(2, 3); // 2^3 -> 8
Math.sqrt(16); // 4

Special values

0.1 + 0.2 === 0.3

Returns false due to floating-point precision. Use rounding or Number.EPSILON for comparisons.

Number.isNaN(NaN)

Returns true. Always use Number.isNaN instead of === because NaN === NaN is false.

Number.isFinite(Infinity)

Returns false. Infinity and -Infinity are not finite numbers.

Number.isInteger(42)

Returns true for whole numbers without a fractional part.

Number.isSafeInteger(9007199254740992)

Returns false. Safe integers are those that can be exactly represented as a double.