Svelte todo app bug: new todos id property is never greater than 2

问题

I am working on a small ToDo application in Svelte for learning purposes (Im new to Svelte).

I have this code for adding a new todo:

<script>
    import { onMount } from "svelte";
      
    let todos = [];
      
    onMount(async function() {
        todos.reverse();
    });
      
    function addTodo() {
        //Empty todo object
        let newTodo = {};
      
        //Set new todo object's properties (id, title, completed)
        if (todos.length == 0) {
            newTodo.id = 1;
        } else {
            newTodo.id = todos[todos.length - 1].id + 1;
        }
        newTodo.title = document.querySelector('#new_todo').value;
        newTodo.completed = false;
      
        //Add new todo at the beginning of the array
        todos.unshift(newTodo);
      
        todos = todos;
    }
</script>

<div class="input-group p-2">
    <input type="text" class="form-control" id="new_todo">
    <div class="input-group-append">
        <button on:click="{addTodo}" class="btn btn-sm btn-success">Add</button>
    </div>
</div>

For a reason I was unable to find - the maximum id of my todos is 2 - no meter how many I add.

See the REPL here.

Where is my mistake?

回答1:

Seems complicated and brittle to me, why not just remember the last insert ID?

// ...
    
let todos = [];
let lastInsertId = 0;
    
function addTodo(){
    //Empty todo object
    let newTodo = {};
        
    //Set new todo object's properties (id, title, completed)
    newTodo.id = ++lastInsertId;
    newTodo.title = document.querySelector('#new_todo').value;
    newTodo.completed = false;
        
    //Add new todo at the behining
    todos.unshift(newTodo);
    todos = todos;
}

// ...

Also why unshift() and reverse() instead of just not reversing and pushing onto the list?

回答2:

change

newTodo.id = todos[todos.length - 1].id + 1;

to

newTodo.id = todos[0].id + 1;

since your first todos have the greatest id, not the last.

来源：https://stackoverflow.com/questions/62659747/svelte-todo-app-bug-new-todos-id-property-is-never-greater-than-2