How to create different slug using same title by incrementing number at end in react

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Javascript

React

let slug = state.data.title.trim().replaceAll(" ", "-").toLowerCase();

what i should get after adding multiple posts using the same title

title
title-1
title-2
title-3

what I get
title
title
title
title

I am using Axios and JSON server

data.json -

{
"posts": [
{
"id": 1,
"title": "title",
"slug": "slug"
},
{
"id": 2,
"title": "title",
"slug": "slug"
},
{
"id": 3,
"title": "title",
"slug": "slug"
}
]
}

What I have tried:

{
    "posts": [
        {
          "id": 1,
          "title": "title",
          "slug": "slug"
        },
        {
          "id": 2,
          "title": "title",
          "slug": "slug"
        },
        {
          "id": 3,
          "title": "title",
          "slug": "slug"
        }
      ]
    }