使用parseFloat方法将字符串解析为浮点数:

parseFloat(num1) + parseFloat(num2)

如果你需要把两个非常大的字符串加在一起，你需要在每个字符串位置计算加法:

function addStrings(str1, str2){
  str1a = str1.split('').reverse();
  str2a = str2.split('').reverse();
  let output = '';
  let longer = Math.max(str1.length, str2.length);
  let carry = false;
  for (let i = 0; i < longer; i++) {
    let result
    if (str1a[i] && str2a[i]) {
      result = parseInt(str1a[i]) + parseInt(str2a[i]);

    } else if (str1a[i] && !str2a[i]) {
      result = parseInt(str1a[i]);

    } else if (!str1a[i] && str2a[i]) {
      result = parseInt(str2a[i]);
    }

    if (carry) {
        result += 1;
        carry = false;
    }
    if(result >= 10) {
      carry = true;
      output += result.toString()[1];
    }else {
      output += result.toString();
    }
  }
  output = output.split('').reverse().join('');

  if(carry) {
    output = '1' + output;
  }
  return output;
}

使用parseFloat方法将字符串解析为浮点数:

parseFloat(num1) + parseFloat(num2)

我总是减去0。

num1-0 + num2-0;

假定一元操作符方法少了一个字符，但并不是每个人都知道一元操作符是什么，或者当他们不知道它被称为什么的时候如何谷歌来找出它。

可以使用parseInt将字符串解析为数字。为了安全起见，始终传递10作为以10为基数解析的第二个参数。

num1 = parseInt(num1, 10);
num2 = parseInt(num2, 10);
alert(num1 + num2);

我在我的项目中使用了这个。我使用+符号处理字符串作为一个数字(在with_interest变量)

<script>
function computeLoan(){
var amount = document.getElementById('amount').value;
var interest_rate = document.getElementById('interest_rate').value;
var days = document.getElementById('days').value;
var interest = (amount * (interest_rate * .01)) / days;
var payment = ((amount / days) + interest).toFixed(2);
var with_interest = (amount * (interest_rate * .01));
var with_interesst = (+amount * (interest_rate * .01)) + (+amount);
payment = payment.toString().replace(/\B(?=(\d{3})+(?!\d))/g, ",");
document.getElementById('payment').innerHTML = "Target Daily = PHP"+payment;
document.getElementById('with_interesst').innerHTML = "Amount w/Interest =   PHP"+with_interesst;
}
</script>

<div name="printchatbox" id="printchatbox">
 <form id="Calculate" class="form-horizontal">
   <h2>You Can Use This Calculator Before Submit </h2>
   <p>Loan Amount: PHP<input id="amount" type="number" min="1" max="1000000"  onchange="computeLoan()"></p>
   <p>Interest Rate: <input id="interest_rate" type="number" min="0" max="100" value="10" step=".1" onchange="computeLoan()">%</p>
    <p>Term<select id="days" type="number" min="1" max="72" step=".1" onchange="computeLoan()">
    <option value="40">40 Days</option>
    <option value="50">50 Days</option>
    <option value="60">60 Days</option>
    <option value="70">70 Days</option>
    <option value="80">80 Days</option>
    <option value="90">90 Days</option>
    <option value="100">100 Days</option>
    <option value="120">120 Days</option>
    </select>
    </p>                        
   <h2 id="payment"></h2>
   <h2 id ="with_interesst"></h2>
 </form>
</div>

希望能有所帮助