src/third_party/mozjs-45/js/src/tests/ecma_6/Map/symbols.js

/* Any copyright is dedicated to the Public Domain.
 * http://creativecommons.org/licenses/publicdomain/ */

var m = new Map;

// Symbols can be Map keys.
var sym = Symbol();
m.set(sym, "zero");
assertEq(m.has(sym), true);
assertEq(m.get(sym), "zero");
assertEq(m.has(Symbol()), false);
assertEq(m.get(Symbol()), undefined);
assertEq([...m][0][0], sym);
m.set(sym, "replaced");
assertEq(m.get(sym), "replaced");
m.delete(sym);
assertEq(m.has(sym), false);
assertEq(m.size, 0);

// Symbols returned by Symbol.for() can be Map keys.
for (var word of "that that is is that that is not is not is that not it".split(' ')) {
    sym = Symbol.for(word);
    m.set(sym, (m.get(sym) || 0) + 1);
}
assertDeepEq([...m], [
    [Symbol.for("that"), 5],
    [Symbol.for("is"), 5],
    [Symbol.for("not"), 3],
    [Symbol.for("it"), 1]
]);

if (typeof reportCompare === "function")
  reportCompare(0, 0);