Get ISO string from a date without time zone

It’s very unclear what you’re asking. If you want the UTC date with the hours always 0, then set the UTC hours to 0 and use toISOString, e.g.

var d = new Date();
d.setUTCHours(0,0,0,0);
console.log(d.toISOString());

Of course this is going to show the UTC date, which may be different to the date on the system that generated the Date.

Also,

new Date('2017-04-27').toISOString();

should return 2017-04-27T00:00:00Z (i.e. it should be parsed as UTC according to ECMA-262, which is contrary to ISO 8601 which would treat it as local), however that is not reliable in all implementations in use.

If you just want to get the current date in ISO 8601 format, you can do:

if (!Date.prototype.toISODate) {
  Date.prototype.toISODate = function() {
    return this.getFullYear() + '-' +
           ('0'+ (this.getMonth()+1)).slice(-2) + '-' +
           ('0'+ this.getDate()).slice(-2);
  }
}

console.log(new Date().toISODate());

However, since the built-in toISOString uses UTC this might be confusing. If the UTC date is required, then:

if (!Date.prototype.toUTCDate) {
  Date.prototype.toUTCDate = function() {
    return this.getUTCFullYear() + '-' +
           ('0'+ (this.getUTCMonth()+1)).slice(-2) + '-' +
           ('0'+ this.getUTCDate()).slice(-2);
  }
}

console.log(new Date().toUTCDate());