inverseLerp function

Computes where a value sits between two numbers: the inverse of lerp. Not clamped.

import { inverseLerp } from 'utils';

Signature

export function inverseLerp(start: number, end: number, value: number): number

Parameters

Name	Description
start	The value mapped to 0.
end	The value mapped to 1.
value	The value to locate.

Returns

The interpolation factor; 0 when start === end.

Example

inverseLerp(0, 10, 5); // 0.5
inverseLerp(10, 0, 2.5); // 0.75

Tests

Line coverage: 100 %.

• ✅ places 0 → 10 at 5 as 0.5
• ✅ places 10 → 0 at 5 as 0.5
• ✅ places 0 → 10 at 20 as 2
• ✅ places 5 → 5 at 5 as 0
• ✅ places 5 → 5 at 100 as 0

Source

src/math/inverse-lerp.ts (on GitHub)

Used by

• remap: Maps a value from an input range to an output range, such as a sensor reading to a gauge angle.

Source code

/**
 * Computes where a value sits between two numbers: the inverse of `lerp`. Not clamped.
 *
 * @param start - The value mapped to 0.
 * @param end - The value mapped to 1.
 * @param value - The value to locate.
 * @returns The interpolation factor; `0` when `start === end`.
 * @example
 * inverseLerp(0, 10, 5); // 0.5
 * inverseLerp(10, 0, 2.5); // 0.75
 */
export function inverseLerp(start: number, end: number, value: number): number {
  const span = end - start;
  return span === 0 ? 0 : (value - start) / span;
}

Test file

import { inverseLerp } from './inverse-lerp';

describe(inverseLerp, () => {
  it.for([
    [0, 10, 5, 0.5],
    [10, 0, 5, 0.5],
    [0, 10, 20, 2],
    [5, 5, 5, 0],
    [5, 5, 100, 0],
  ] as const)('places %s → %s at %s as %s', ([start, end, value, expected]) => {
    expect(inverseLerp(start, end, value)).toBe(expected);
  });
});

Keywords: inverse, lerp, math, function