inexact-mapping-flaw.js

let map;

function setup(phone1, phone2) {
    map[phone1] = phone2;
    map[phone2] = phone1;
}

function teardown(phone1, phone2) {
    delete map[phone1];
    delete map[phone2];
}

function print(map) {
    println('======');
    Object.keys(map).forEach(k => {
        const v = map[k];
        println(`${k} >> ${v}`);
    });
}

function println(str) {
    process.stdout.write(str + '\n');
}

map = Object.create(null);

setup('A', 'B');
print(map);
/* A and B can reach each other */

setup('A', 'C');
print(map);
/* A can reach C, (ok)
   B can reach A, (bad)
   C can reach A, (ok)
   but A can not reach B (orphan mapping) */

teardown('A', 'B');
print(map);
/* C can reach A only, and is now only orphan mapping. */

A >> B
B >> A

A >> C
B >> A
C >> A

C >> A