MapComplete/UI/Base/If.svelte

<script lang="ts">
  import { UIEventSource } from "../../Logic/UIEventSource";
  import { onDestroy } from "svelte";

  /**
   * For some stupid reason, it is very hard to let {#if} work together with UIEventSources, so we wrap then here
   */
  export let condition: UIEventSource<boolean>;
  let _c = condition.data;
  onDestroy(condition.addCallback(c => {
    /* Do _not_ abbreviate this as `.addCallback(c => _c = c)`. This is the same as writing `.addCallback(c => {return _c = c})`, 
    which will _unregister_ the callback if `c = true`! */
    _c = c;
    return false
  }))
  
</script>

{#if _c}
  <slot></slot>
  {:else}
  <slot name="else"></slot>
{/if}