hamjest/lib/matchers/IsCloseTo.js

A library of composable matchers for defining meaningful and readable assertions in JavaScript.

'use strict';

const _create = require('lodash/create');
const IsNumber = require('./IsNumber');
const assertThat = require('../assertThat');
const is = require('./Is').is;
const number = require('./IsNumber').number;

function IsCloseTo(threshold, delta) {
	assertThat(threshold, is(number()));
	assertThat(delta, is(number()));

	function getDelta(actual) {
		return Math.abs(actual - threshold);
	}

	return _create(new IsNumber(), {
		matchesSafely: function (actual) {
			return getDelta(actual) <= delta;
		},
		describeTo: function (description) {
			description
				.append('a number within ')
				.appendValue(delta)
				.append(' of ')
				.appendValue(threshold);
		},
		describeMismatchSafely: function (actual, description) {
			description
				.appendValue(actual)
				.append(' differed by ')
				.appendValue(getDelta(actual));
		}
	});
}

IsCloseTo.closeTo = function (threshold, delta) {
	return new IsCloseTo(threshold, delta);
};

module.exports = IsCloseTo;