Truncate a number to a given number of decimal places without rounding

JavaScript

const toFixed = (n, fixed) => `${n}`.match(new RegExp(`^-?\\d+(?:\.\\d{0,${fixed}})?`))[0]

// Or
const toFixed = (n, fixed) => ~~(Math.pow(10, fixed) * n) / Math.pow(10, fixed)

TypeScript

const toFixed = (n: number, fixed: number): number => +(`${n}`.match(new RegExp(`^-?\\d+(?:\.\\d{0,${fixed}})?`)) as string[])[0]

// Or
const toFixed = (n: number, fixed: number): number => ~~(Math.pow(10, fixed) * n) / Math.pow(10, fixed)

Examples

toFixed(25.198726354, 1) // 25.1
toFixed(25.198726354, 2) // 25.19
toFixed(25.198726354, 3) // 25.198
toFixed(25.198726354, 4) // 25.1987
toFixed(25.198726354, 5) // 25.19872
toFixed(25.198726354, 6) // 25.198726