world-population/dist/index.js

World Population Counter, based on UN World Population Prospects data

"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
exports.estimateDate = exports.interval = exports.estimate = void 0;
const data_1 = require("./data");
/**
 * Look up an UN estimated population for a specific year
 */
function lookupPopulation(date) {
    const result = data_1.estimates.find((e) => e.year == date.getFullYear());
    if (result) {
        return result.pop * 1000;
    }
    else {
        throw new Error("Year out of range.");
    }
}
/**
 * Estimate the world population at a moment in time. Defaults to now.
 */
function estimate(date = new Date()) {
    const start = new Date(date.getFullYear(), 0);
    const end = new Date(date.getFullYear() + 1, 0);
    const startPop = lookupPopulation(start);
    const endPop = lookupPopulation(end);
    const increase = endPop - startPop;
    const progress = (date.getTime() - start.getTime()) / (end.getTime() - start.getTime());
    return Math.round(startPop + increase * progress);
}
exports.estimate = estimate;
/**
 * The average number of milliseconds between each birth at a moment in time.
 * Defaults to now. Useful for incrementing counters.
 */
function interval(date = new Date()) {
    const start = new Date(date.getFullYear(), 0);
    const end = new Date(date.getFullYear() + 1, 0);
    const startPop = lookupPopulation(start);
    const endPop = lookupPopulation(end);
    const increase = endPop - startPop;
    const length = end.getTime() - start.getTime();
    return Math.round(length / increase);
}
exports.interval = interval;
/**
 * Estimate the date that the population will reach a certain value (for the
 * first time)
 * @param population
 */
function estimateDate(population) {
    const populationThousands = population / 1000;
    // Find first year with a population larger that the population.
    const after = data_1.estimates.find((n) => n.pop > populationThousands);
    if (!after) {
        throw new Error("Population not predicted to reach " + population);
    }
    // And the year before.
    const before = data_1.estimates.find((n) => n.year == after.year - 1);
    if (!before) {
        throw new Error("Data not available.");
    }
    // Assuming linear growth, what percentage of the year will have elapsed
    // before we reach the population?
    const percentageThroughYear = (populationThousands - before.pop) / (after.pop - before.pop);
    // How many milliseconds are there in this year?
    const start = new Date(before.year, 0);
    const end = new Date(after.year, 0);
    const milliseconds = end.getTime() - start.getTime();
    // Calculate the instant we will hit this population.
    const instant = new Date(start.getTime() + milliseconds * percentageThroughYear);
    return instant;
}
exports.estimateDate = estimateDate;