Solution to JS out-of-precision number problem

// js maximum safe number: Math.pow(2, 53)-1

let a = '123456444565456.889'
let b = '121231456.32'
// a + b = '123456565796913.209'

function addTwo(a, b) {
    //1. Compare the lengths of two numbers and add 0 to the front of the shorter one
    if (a.length > b.length) {
        let arr = Array(a.length - b.length).fill(0);
        b = arr.join('') + b
    } else if (a.length < b.length) {
        let arr = Array(b.length - a.length).fill(0);
        a = arr.join('') + a
    }

    //2. Reverse the two numbers (this is because people are used to adding from left to right, but numbers are added from right to left, so reversing them is easier to understand)
    a = a.split('').reverse();
    b = b.split('').reverse();

    //3. Loop through two arrays and add them. If the sum is greater than 10, then sign = 1, and the value at the current position is (sum % 10)
    let sign = 0; //mark whether there is carry let newVal = []; //used to store the final result for (let j = 0; j < a.length; j++) {
        let val = a[j] / 1 + b[j] / 1 + sign; // Divide by 1 to ensure that they are all numbers. You can also use Number() here.
        if (val >= 10) {
            sign = 1;
            newVal.unshift(val % 10) // unshift is used here instead of push because it saves the need to use reverse
        } else {
            sign = 0;
            newVal.unshift(val)
        }
    }

    // The last addition needs to add a digit '1'
    return sign && newVal.unshift(sign) && newVal.join('') || newVal.join('')
}

// Refer to other friends' concise writing function addTwo(a,b) {
    let temp = 0
    let res = ''
    a = a.split('')
    b = b.split('')
    while(a.length || b.length || temp) {
        temp += Number(a.pop() || 0) + Number(b.pop() || 0)
        res = (temp%10) + res
        temp = temp > 9
    }
    return res.replace(/^0+/g, '')
}

let a = '123456444565456.889'
let b = '121231456.32'
// a + b = '123456565796913.209'

function addTwo(a = '0',b = '0', isHasDecimal=false) {
    //1. Compare the lengths of two numbers and add 0 to the front of the shorter one
    if (a.length > b.length) {
        let arr = Array(a.length - b.length).fill(0);
        b = isHasDecimal && (b + arr.join('')) || arr.join('') + b
    } else if (a.length < b.length) {
        let arr = Array(b.length - a.length).fill(0);
        a = isHasDecimal && (a + arr.join('')) || arr.join('') + a
    }

    //2. Reverse the two numbers (this is because people are used to adding from left to right, but numbers are added from right to left, so reversing them is easier to understand)
    a = a.split('').reverse();
    b = b.split('').reverse();


    //3. Loop through two arrays and add them. If the sum is greater than 10, then sign = 1, and the value at the current position is (sum % 10)
    let sign = 0; //mark whether there is carry let newVal = []; //used to store the final result for (let j = 0; j < a.length; j++) {
        let val = a[j] / 1 + b[j] / 1 + sign; // Divide by 1 to ensure that they are all numbers. You can also use Number() here.
        if (val >= 10) {
            sign = 1;
            newVal.unshift(val % 10) // unshift is used here instead of push because it saves the need to use reverse
        } else {
            sign = 0;
            newVal.unshift(val)
        }
    }

    // The last addition needs to add a digit '1'
    return sign && newVal.unshift(sign) && newVal.join('') || newVal.join('')
}

function add(a,b) {
    let num1 = String(a).split('.')
    let num2 = String(b).split('.')
    let intSum = addTwo(num1[0], num2[0])
    let res = intSum

    if (num1.length>1 || num2.length > 1) {
        let decimalSum = addTwo(num1[1], num2[1], true)

        if (decimalSum.length > (num1[1]||'0').length && decimalSum.length > (num2[1]||'0').length) {
            intSum = addTwo(intSum, decimalSum[0])
            decimalSum = decimalSum.slice(1)
            res = `${intSum}.${decimalSum}`
        } else {
            res = `${intSum}.${decimalSum}`
        }
    }
    return res
}
console.log(add(a, b)) // 123456565796913.209
// console.log(add('325', '988')) // 1313