exact-target.js

import { helper } from 'ember-helper';
import $ from 'jquery';

export default helper(function([selector, handler]) {
  return function(event) {
    if ($(event.target).is(selector) && handler) {
      return handler(event);
    }
  };
});

modal-target.hbs

<div class="modal">
  {{#with-sidebar name="modal" as |modalContent hooks|}}
    {{#if modalContent}}
      <div class="modal-backdrop"></div>
      <div class="modal-container" onclick={{action (exact-target ".modal-container" hooks.outsideClick) }}>
        <div class="modal-dialog" >
          {{component modalContent}}
        </div>
      </div>
    {{/if}}
  {{/with-sidebar}}
</div>

modal.css

.modal-backdrop {
    position: fixed;
    top: 0;
    width: 100vw;
    height: 100vh;
    background-color: black;
    opacity: 0.8;
    z-index: 12;
}
.modal-container {
    position: fixed;
    top: 0;
    width: 100vw;
    height: 100vh;
    z-index: 13;
    display: flex;
    align-items: center;
    justify-content: center;
}
.modal-dialog {
    background-color: white;
    border-radius: 4px;
    max-height: 100vh;
    overflow-y: auto;
}

usage.hbs

{{#if showUploader}}
  {{in-sidebar name="modal"
               show=(component "image-upload-modal" imagesReady=(action "imageReady"))
               hooks=(hash outsideClick=(action (mut showUploader) false))   }}
{{/if}}