Why are split and join results are different?

Question

I used split and join to swap latitude and longitude of the coordinates. I am using leaflet to get the coordinates and as polyline, swapping coordinates works just fine but when I do it using marker, the last digit of the latitude and first digit of longitude is gone
This is the code, as you can see they're just the same code

if (type === 'polyline') {
    const res = ["[" +
      tmp.map(
        x => '[' +
        swapLatLon(
          stripFirstLast(x).split(', ')
        ).join(', ') +
        ']'
      ).join(', ') +
      "]"
    ];
  document.getElementById("polyline").value = res;
} else if (type === 'marker') {
    const res = ["[" +
      tmp.map(
        x => '[' +
        swapLatLon(
          stripFirstLast(x).split(', ')
        ).join(', ') +
        ']'
      ).join(', ') +
      "]"
    ];
  document.getElementById("marker").value = res;
} else {
  console.log('__undefined__');
}

This is a sample result for res

Original: [37.0902, 95.7129]
Expectation: [[95.7129, 37.0902]]
Reality: [[95.712, 7.0902]]

Answer 1

split and join are inverses of each other. It is likely that the issue is elsewhere in the data processing.

In any case, here is a direct one line solution using the data examples that you provided:

x = "[37.0902, 95.7129]"
swapped = "[" + x.slice(1,-1).split(", ").reverse().join(", ") + "]"

Answer 2

If you only want to swap places of two variables in an array, then use deconstructing.

const tmp = [37.0902, 95.7129]
let [long, lat] = tmp;
let res = [[lat, long]];
let type;

if (type === 'polyline') {
  document.getElementById("polyline").value = res;
} else if (type === 'marker') {
  document.getElementById("marker").value = res;
} else {
  console.log('__undefined__');
}

console.log({tmp})
console.log({res})