round

Rounds a number to a specified number of decimal places. Performs precise rounding by scaling the number, applying Math.round, then scaling back. Handles floating-point precision issues better than naive approaches. Supports both positive precision (decimal places) and negative precision (rounding to tens, hundreds, etc.).

Signature

const round: (value: number, precision?: number) => number

Parameters

Name	Type	Description
value	-	Number to round
precision	-	Number of decimal places (default: 0), can be negative

Returns

Rounded number with specified precision

Examples

Basic rounding operations

import { round } from '@winglet/common-utils';

// Default (integer rounding)
console.log(round(3.7)); // 4
console.log(round(3.2)); // 3
console.log(round(-2.6)); // -3

// Decimal precision
console.log(round(3.14159, 2)); // 3.14
console.log(round(2.678, 1)); // 2.7
console.log(round(1.005, 2)); // 1.01

Advanced precision and edge cases

// Negative precision (round to tens, hundreds)
console.log(round(1234, -1)); // 1230 (round to nearest 10)
console.log(round(1234, -2)); // 1200 (round to nearest 100)
console.log(round(1234, -3)); // 1000 (round to nearest 1000)

// High precision
console.log(round(0.123456789, 5)); // 0.12346
console.log(round(Math.PI, 4)); // 3.1416

// Edge cases
console.log(round(0, 5)); // 0
console.log(round(0.5, 0)); // 1 (rounds half up)

Playground

import { round } from '@winglet/common-utils';

// Default (integer rounding)
console.log(round(3.7)); // 4
console.log(round(3.2)); // 3
console.log(round(-2.6)); // -3

// Decimal precision
console.log(round(3.14159, 2)); // 3.14
console.log(round(2.678, 1)); // 2.7
console.log(round(1.005, 2)); // 1.01

Notes

Rounding Behavior:

• Uses "round half away from zero" method (Math.round behavior)
• Positive precision: decimal places (1 = 0.1, 2 = 0.01)
• Negative precision: powers of 10 (-1 = 10, -2 = 100)
• Zero precision: rounds to nearest integer

Use Cases:

• Financial calculations (currency rounding)
• Display formatting for user interfaces
• Scientific calculations with precision requirements
• Data processing and statistical analysis
• Configuration values with limited precision
• API responses requiring standardized decimal places

Performance: O(1) time and space complexity - constant time operations. More reliable than simple decimal truncation or naive rounding approaches.