numerical-direction.mjs

const numericalDirection = (arg, n = Number(arg)) => Math.abs(n) / n || 0

export default numericalDirection;

numerical-direction.test.mjs

import test from 'node:test';
import assert from 'node:assert/strict';
import numericalDirection from './index.js'

test('positive numbers return 1', (t) => {
    const expected = 1
    assert.strictEqual(numericalDirection(1), expected);
    assert.strictEqual(numericalDirection(2), expected);
    assert.strictEqual(numericalDirection(3), expected);
    assert.strictEqual(numericalDirection(10), expected);
    assert.strictEqual(numericalDirection(999999), expected);
    assert.strictEqual(numericalDirection(.1), expected);
    assert.strictEqual(numericalDirection(.000000000000001), expected);
    assert.strictEqual(numericalDirection(Math.PI), expected);
    assert.strictEqual(numericalDirection(Math.E), expected);
    assert.strictEqual(numericalDirection(Number.MAX_SAFE_INTEGER), expected);
});

test('negative numbers return -1', (t) => {
    const expected = -1
    assert.strictEqual(numericalDirection(-1), expected);
    assert.strictEqual(numericalDirection(-2), expected);
    assert.strictEqual(numericalDirection(-3), expected);
    assert.strictEqual(numericalDirection(-10), expected);
    assert.strictEqual(numericalDirection(-999999), expected);
    assert.strictEqual(numericalDirection(-.1), expected);
    assert.strictEqual(numericalDirection(-.000000000000001), expected);
    assert.strictEqual(numericalDirection(-Math.PI), expected);
    assert.strictEqual(numericalDirection(-Math.E), expected);
    assert.strictEqual(numericalDirection(Number.MIN_SAFE_INTEGER), expected);
});

test('0 returns 0', (t) => {
    assert.strictEqual(numericalDirection(0), 0);
});

test('-0 returns 0', (t) => {
    assert.strictEqual(numericalDirection(-0), 0);
});

test('NaN returns 0', (t) => {
    assert.strictEqual(numericalDirection(NaN), 0);
});

test('Arguments that parse to NaN reutrn 0', (t) => {
    const expected = 0
    assert.strictEqual(numericalDirection(NaN), expected);
    assert.strictEqual(numericalDirection('NaN'), expected);
    assert.strictEqual(numericalDirection('Hello'), expected);
    assert.strictEqual(numericalDirection({}), expected);
    assert.strictEqual(numericalDirection([]), expected);
    assert.strictEqual(numericalDirection(undefined), expected);
    assert.strictEqual(numericalDirection(null), expected);
    assert.strictEqual(numericalDirection(void 1), expected);
    assert.strictEqual(numericalDirection(false), expected);
});

test('Arguments parsable as positive numbers returns 1', (t) => {
    const expected = 1;
    assert.strictEqual(numericalDirection('1'), expected);
    assert.strictEqual(numericalDirection('2'), expected);
    assert.strictEqual(numericalDirection('3'), expected);
    assert.strictEqual(numericalDirection('10'), expected);
    assert.strictEqual(numericalDirection('999999'), expected);
    assert.strictEqual(numericalDirection('.1'), expected);
    assert.strictEqual(numericalDirection('0.1'), expected);
    assert.strictEqual(numericalDirection('.000000000000001'), expected);
    assert.strictEqual(numericalDirection(String(Math.PI)), expected);
    assert.strictEqual(numericalDirection(String(Math.E)), expected);
    assert.strictEqual(numericalDirection(String(Number.MAX_SAFE_INTEGER)), expected);
    assert.strictEqual(numericalDirection(true), expected);
});

test('Arguments parsable as negative numbers returns -1', (t) => {
    const expected = -1
    assert.strictEqual(numericalDirection('-1'), expected);
    assert.strictEqual(numericalDirection('-2'), expected);
    assert.strictEqual(numericalDirection('-3'), expected);
    assert.strictEqual(numericalDirection('-10'), expected);
    assert.strictEqual(numericalDirection('-999999'), expected);
    assert.strictEqual(numericalDirection('-.1'), expected);
    assert.strictEqual(numericalDirection('-0.1'), expected);
    assert.strictEqual(numericalDirection('-.000000000000001'), expected);
    assert.strictEqual(numericalDirection(String(-Math.PI)), expected);
    assert.strictEqual(numericalDirection(String(-Math.E)), expected);
    assert.strictEqual(numericalDirection(String(Number.MIN_SAFE_INTEGER)), expected);
});

test('Arguments parsable as 0 returns 0', (t) => {
    assert.strictEqual(numericalDirection('0'), 0);
});

test('Arguments parsable as -0 returns 0', (t) => {
    assert.strictEqual(numericalDirection('-0'), 0);
});