Array

1. 数组存在该项replace不存在push

function pushToArray(arr, obj) {
    const index = arr.findIndex((e) => e.id === obj.id);
    if (index === -1) {
        arr.push(obj);
    } else {
        arr[index] = obj;
    }
}

Determine whether to push or update object in array based on unique ID

2. slice/splice

Slice 不改变原数组

let bread = ['loaf1','loaf2','loaf3','loaf4','loaf5','loaf6'];
newArr = bread.slice(2, 5);
console.log(newArr); // [ 'loaf3', 'loaf4', 'loaf5' ]

Splice leads to mutation of the origin array

1. 只删除 ```javascript let bread = [‘loaf1’,’loaf2’,’loaf3’,’loaf4’,’loaf5’,’loaf6’]; bread.splice(1, 3); console.log(bread); // [“loaf2”, “loaf3”, “loaf4”]

2. Removing and adding new element
```javascript
let bread = ['loaf1','loaf2','loaf3','loaf4','loaf5','loaf6'];
bread.splice(1, 3, 'newLoaf1', 'newLoaf2');
console.log(bread);
// ["loaf1", "newLoaf1", "newLoaf2", "loaf5", "loaf6"]

1. Only adding new element

   let bread = ['loaf1','loaf2','loaf3','loaf4','loaf5','loaf6'];
   bread.splice(3, 0, 'newLoaf1', 'newLoaf2');
   console.log(bread);
   // ["loaf1", "loaf2", "loaf3", "newLoaf1", "newLoaf2", "loaf4", "loaf5", "loaf6"]
   

   Array.slice 8 种不同用法