Array of objects count and update numbering only if the boolean of top row is true

Question

I'm struggling to get the following to work.

I have a sorted array of objects which contains No,Title, and Top (Which means the top row):

var arr = [];
arr = [
    {No: "", Title: "John", Top: true},
    {No: "", Title: "John", Top: false},
    {No: "", Title: "John", Top: false},
    {No: "", Title: "Kyle", Top: true},
    {No: "", Title: "Jonnah", Top: true},
    {No: "", Title: "Jonnah", Top: false},
    {No: "", Title: "Hyuri", Top: true},
    {No: "", Title: "Hyuri", Top: false},
    {No: "", Title: "Hyuri", Top: false},
]

I want to count and update the numbering No only if the Top is true.

So, below is the results that I expected to get:

arr = [
    {No: "1", Title: "John", Top: true},
    {No: "", Title: "John", Top: false},
    {No: "", Title: "John", Top: false},
    {No: "2", Title: "Kyle", Top: true},
    {No: "3", Title: "Jonnah", Top: true},
    {No: "", Title: "Jonnah", Top: false},
    {No: "4", Title: "Hyuri", Top: true},
    {No: "", Title: "Hyuri", Top: false},
    {No: "", Title: "Hyuri", Top: false},
]

Following is an attempt I've made:

for(var i=0;i<arr.length;i++){
    if(i!=(arr.length-1)){
        if(arr[i].Top){
            arr[i].No = i+1;
        }else{
            arr[i+1].No = arr[i].No;
        }
    }
    
}

The results that i get:

[
    {"No": 1, "Title": "John", "Top": true},
    {"No": "", "Title": "John", "Top": false},
    {"No": "", "Title": "John", "Top": false},
    {"No": 4, "Title": "Kyle", "Top": true},
    {"No": 5, "Title": "Jonnah", "Top": true},
    {"No": "", "Title": "Jonnah", "Top": false},
    {"No": 7, "Title": "Hyuri", "Top": true},
    {"No": "", "Title": "Hyuri", "Top": false},
    {"No": "", "Title": "Hyuri", "Top": false}
]

How can i get the results that i want?

Answer 1

You could take a closure over count and update the object, if necessary.

const
    data = [{ No: "", Title: "John", Top: true }, { No: "", Title: "John", Top: false }, { No: "", Title: "John", Top: false }, { No: "", Title: "Kyle", Top: true }, { No: "", Title: "Jonnah", Top: true }, { No: "", Title: "Jonnah", Top: false }, { No: "", Title: "Hyuri", Top: true }, { No: "", Title: "Hyuri", Top: false }, { No: "", Title: "Hyuri", Top: false }],
    result = data.map((count => o => ({
        ...o,
        ...o.Top && { No: (++count).toString() }
    }))(0));

console.log(result);

.as-console-wrapper { max-height: 100% !important; top: 0; }