Answers for "deal with 8 decimal places without rounding js"

javascript round to 8 decimal places

>>> parseFloat(0.9999999.toFixed(4));
1
>>> parseFloat(0.0009999999.toFixed(4));
0.001
>>> parseFloat(0.0000009999999.toFixed(4));
0

javascript truncate decimal without rounding

// truncate function
// in this example the default value is 2
function truncate(number, index = 2) {
  	// cutting the number
    return +number.toString().slice(0, (number.toString().indexOf(".")) + (index + 1));
}

// example
console.log(truncate(1234.56789, 3)); // 1234.567