var h = 3;

console.log(j(h,function(x){
    return [(new String(' ')).repeat(h-(x)), (new String('#')).repeat(x), ' ', (new String('#')).repeat(x)].join('');
}));

function j(h,provider) {
    let value = [];
    (new Array(h)).fill(0).forEach(function(v,i){
        value[i]=provider(i+1);
    });
    return value.join('\n');
}