Like this:

var val = 37.435345;

var countDecimals = function(value) {

  let text = value.toString()

  // verify if number 0.000005 is represented as "5e-6"

  if (text.indexOf('e-') > -1) {

    let [base, trail] = text.split('e-');

    let deg = parseInt(trail, 10);

    return deg;

  }

  // count decimals for number in representation like "0.123456"

  if (Math.floor(value) !== value) {

    return value.toString().split(".")[1].length || 0;

  }

  return 0;

}

countDecimals(val);