Javascript - I can't figure out what's going on. I add an object to the array, it is added, but the old data copies the values from the new object

YT
March 3, 2024
203 views
0 votes
2 Answers

I can’t figure out what’s going on. I add an object to the array, it is added, but the old data copies the values from the new object. This is the first time I’ve encountered this.

Here is the code

      var news = []
      var next
      if(cart === null){
        next = 0
      }else {
        next = cart.length
      }
      switch(type){
        case 'horizontal':
          config['0']['type'] = type
          config['0']['id'] = next
          config['0'].idImg = selectSvg
          if(cart === null || cart === undefined || cart.length < 1){
            news.push(config)
            setCountCart(news.length)
            localStorage.setItem('cart-tagstyle', JSON.stringify(news))
            setCart(news)
          }else {
            var news = cart.slice()
            console.log(news);
            news.push(config)
            console.log(news);
            setCountCart(news.length)
            localStorage.setItem('cart-tagstyle', JSON.stringify(news))
            setCart(news)
          }
          break;

I tried it without push, according to the following index, the same thing. I searched the Internet, it didn’t help. I’ve been suffering for the second day

Tags: arrays javascript

Answers

- PanktiShah
- March 3, 2024 at 8:34 am
- 0 votes
0
```
config['0']['type'] = type
config['0']['id'] = next
config['0'].idImg = selectSvg
```
Due to this old data copies value from new objects. Check the below code where the index is changed
```
config[next]['type'] = type
config[next]['id'] = next
config[next].idImg = selectSvg
```
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- AmirHossein_Khakshouri
- March 3, 2024 at 8:53 am
- 0 votes
0
if I understand the problem correctly,
the problem is that because arrays are reference types. Which means when you assign an array to a variable, you’re assigning a memory address and not the actual array itself,
so you should use deep clone for solving that or use
```
const newArray = [...oldArray];
```
than changing newArray will not effects oldArray

checkout this link for more info
https://dev.to/samanthaming/how-to-deep-clone-an-array-in-javascript-3cig
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