如何在 Svelte 中循环每个数组时弹出数组？

Question

<script> 
   let myMessages = ["msg1", "msg2", "msg3"]
</script>

{#each myMessages as message}
    <div>{message}</div>
{/each}

我想在添加到 DOM 后从 myMessages 中删除每个元素，所以最后 myMessages 是空的？
（对此的一个变体是在循环中添加一个 {#if} 条件，并且仅当元素满足此条件时才删除）

Answer 1

Svelte's reactivity system基于赋值运算符=
未检测到数组的突变（使用 pop() 之类的方法）。

myMessages.pop()
myMessages = myMessages // this line will trigger svelte to update the dom

Answer 2

在没有关于 DOM 渲染的反馈的情况下，我会假设它。因此，要呈现 msg1 并在之后弹出它，我将按如下方式进行：

<script> 
  let myMessages = []
  let tmpMessages = myMessages
  # then add msg1 to myMessages, render it and pop it
  myMessages.push("msg1")
  tmpMessages = myMessages
  myMessages.pop()
</script>

{#each tmpMessages as message}
  <div>{message}</div>
{/each}

Answer 3

这可以通过创建一个消息组件来实现，该组件在 created/mounted 时将自己的删除（从数组中删除）分派给父应用程序。像这样，以后可以使用相同的功能将更多消息添加到 myMessages 数组。

Demo REPL

[App.svelte]

<script>
  import { onMount } from 'svelte';
  import Message from './Message.svelte'
    
  let myMessages = ["msg1", "msg2", "msg3"]

// add two additional Messages 1,5s after App creation  
onMount( () => {
    setTimeout(function() {
      myMessages = [...myMessages, "msg4","msg5"];
    }, 1500);
});
    
function deleteMessage(event){
    myMessages = myMessages.slice(1)
    console.log(myMessages)
}   
</script>

{#each myMessages as message}
    <Message {message} on:delete={deleteMessage}/>
{/each}

[Message.svelte]

<script>
    import { onMount } from 'svelte';
    import { createEventDispatcher } from 'svelte';
    const dispatch = createEventDispatcher();

    export let message;
    
onMount( () => {
    setTimeout(function() {
      dispatch('delete', {          
        });
    }, 3000);
}); 
</script>

<div> {message} </div>

或者，因为没有发送信息，只触发了删除，没有像这样发送-> Demo REPL

[App.svelte]

<script>
    import { onMount } from 'svelte';
  import Message from './Message.svelte'
    
    let myMessages = ["msg1", "msg2", "msg3"]
    
// add two additional Messages 1,5s after App creation 
onMount( () => {
    setTimeout(function() {
      myMessages = [...myMessages, "msg4","msg5"];
    }, 1500);
});
    
function deleteMessage() {
    // delete first element in arr
    myMessages = myMessages.slice(1)
    console.log(myMessages)
}   
    
</script>

{#each myMessages as message}
    <Message {message} {deleteMessage} />
{/each}

[Message.svelte]

<script>
    import { onMount } from 'svelte';
    
    export let message;
    export let deleteMessage;
    
onMount( () => {
    setTimeout(function() {
        deleteMessage();
    }, 3000);
}); 
</script>

<div> {message} </div>

如何在 Svelte 中循环每个数组时弹出数组？

How to pop array while looping with each in Svelte?

svelte-3

[App.svelte]

[Message.svelte]

[App.svelte]

[Message.svelte]