Javascript Map delete / set is slow

Could somebody explain, why Map is slower, than Object in the code below?
Docs says, that Map is optimized for performance, but tests shows poor results.

#!/usr/bin/env node

const object = {},
    map = new Map(),
    prefix = "a",
    iteratiions = 100_000;

for ( let n = 0; n < 100_000; n++ ) {
    object[prefix + n] = n;
    map.set( prefix + n, n );
}

const t1 = Date.now();
for ( let n = 0; n < iteratiions; n++ ) {
    map.delete( prefix );
    map.set( prefix, 1 );
}
console.log( "Map:", Date.now() - t1, "ms" );

const t0 = Date.now();
for ( let n = 0; n < iteratiions; n++ ) {
    delete object[prefix];
    object[prefix] = 1;
}
console.log( "object:", Date.now() - t0, "ms" );

Output:

Map: 7558 ms
object: 11 ms