How to add two strings as if they were numbers?
JavascriptJavascript Problem Overview
I have two strings which contain only numbers:
var num1 = '20',
num2 = '30.5';
I would have expected that I could add them together, but they are being concatenated instead:
num1 + num2; // = '2030.5'
How can I force these strings to be treated as numbers?
Javascript Solutions
Solution 1 - Javascript
I would use the unary plus operator to convert them to numbers first.
+num1 + +num2;
Solution 2 - Javascript
MDN docs for parseInt
MDN docs for parseFloat
In parseInt radix is specified as ten so that we are in base 10. In nonstrict javascript a number prepended with 0
is treated as octal. This would obviously cause problems!
parseInt(num1, 10) + parseInt(num2, 10) //base10
parseFloat(num1) + parseFloat(num2)
Also see ChaosPandion's answer for a useful shortcut using a unary operator. I have set up a fiddle to show the different behaviors.
var ten = '10';
var zero_ten = '010';
var one = '1';
var body = document.getElementsByTagName('body')[0];
Append(parseInt(ten) + parseInt(one));
Append(parseInt(zero_ten) + parseInt(one));
Append(+ten + +one);
Append(+zero_ten + +one);
function Append(text) {
body.appendChild(document.createTextNode(text));
body.appendChild(document.createElement('br'));
}
Solution 3 - Javascript
I would recommend to use the unary plus operator, to force an eventual string to be treated as number, inside parenthesis to make the code more readable like the following:
(+varname)
So, in your case it's:
var num1 = '20',
num2 = '30.5';
var sum = (+num1) + (+num2);
// Just to test it
console.log( sum ); // 50.5
Solution 4 - Javascript
var result = Number(num1) + Number(num2);
Solution 5 - Javascript
convert the strings to floats
with parseFloat(string)
or to integers
with parseInt(string)
Solution 6 - Javascript
If you need to add two strings together which are very large numbers you'll need to evaluate the addition at every string position:
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;
}
Solution 7 - Javascript
You can use this to add numbers:
var x = +num1 + +num2;
Solution 8 - Javascript
try
var x = parseFloat(num1) + parseFloat(num2) ;
or, depending on your needs:
var x = parseInt(num1) + parseInt(num2) ;
http://www.javascripter.net/faq/convert2.htm
You might want to pick up the book Javascript: The Good Parts, by Douglas Crockford. Javascript has a rather sizeable colleciton of gotchas! This book goes a long way towards clarifying them. See also
and Mr. Crockford's excellent essay, Javascript: The World's Most Misunderstood Programming Language.
Solution 9 - Javascript
I've always just subtracted zero.
num1-0 + num2-0;
Granted that the unary operator method is one less character, but not everyone knows what a unary operator is or how to google to find out when they don't know what it's called.
Solution 10 - Javascript
function sum(){
var x,y,z;
x = Number(document.getElementById("input1").value);
y = Number(document.getElementById("input2").value);
z = x + y;
document.getElementById("result").innerHTML = z ;
}
Solution 11 - Javascript
If you want to perform operation with numbers as strings (as in the case where numbers are bigger than 64bits can hold) you can use the big-integer library.
const bigInt = require('big-integer')
bigInt("999").add("1").toString() // output: "1000"
Solution 12 - Javascript
Here, you have two options to do this :-
> 1.You can use the unary plus to convert string number into integer. > > 2.You can also achieve this via parsing the number into corresponding type. i.e parseInt(), parseFloat() etc
.
Now I am going to show you here with the help of examples(Find the sum of two numbers).
Using unary plus operator
<!DOCTYPE html>
<html>
<body>
<H1>Program for sum of two numbers.</H1>
<p id="myId"></p>
<script>
var x = prompt("Please enter the first number.");//prompt will always return string value
var y = prompt("Please enter the second nubmer.");
var z = +x + +y;
document.getElementById("myId").innerHTML ="Sum of "+x+" and "+y+" is "+z;
</script>
</body>
</html>
Using parsing approach-
<!DOCTYPE html>
<html>
<body>
<H1>Program for sum of two numbers.</H1>
<p id="myId"></p>
<script>
var x = prompt("Please enter the first number.");
var y = prompt("Please enter the second number.");
var z = parseInt(x) + parseInt(y);
document.getElementById("myId").innerHTML ="Sum of "+x+" and "+y+" is "+z;
</script>
</body>
</html>
Solution 13 - Javascript
You can use parseInt
to parse a string to a number. To be on the safe side of things, always pass 10
as the second argument to parse in base 10.
num1 = parseInt(num1, 10);
num2 = parseInt(num2, 10);
alert(num1 + num2);
Solution 14 - Javascript
Make sure that you round your final answer to less than 16 decimal places for floats as java script is buggy.
For example 5 - 7.6 = -2.5999999999999996
Solution 15 - Javascript
@cr05s19xx suggested on a duplicate question:
JavaScript is a bit funny when it comes to numbers and addition.
Giving the following
'20' - '30' = 10; // returns 10 as a number '20' + '30' = '2030'; // Returns them as a string The values returned from document.getElementById are strings, so it's better to parse them all (even the one that works) to number, before proceeding with the addition or subtraction. Your code can be:
function myFunction() {
var per = parseInt(document.getElementById('input1').value);
var num = parseInt(document.getElementById('input2').value);
var sum = (num / 100) * per;
var output = num - sum;
console.log(output);
document.getElementById('demo').innerHTML = output;
}
function myFunction2() {
var per = parseInt(document.getElementById('input3').value);
var num = parseInt(document.getElementById('input4').value);
var sum = (num / 100) * per;
var output = sum + num;
console.log(output);
document.getElementById('demo1').innerHTML = output;
}
Solution 16 - Javascript
Use the parseFloat
method to parse the strings into floating point numbers:
parseFloat(num1) + parseFloat(num2)
Solution 17 - Javascript
I use this in my project.I use + sign to treat string as a number (in with_interesst variable)
<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>
Hope it helps
Solution 18 - Javascript
document.getElementById(currentInputChoosen).value -= +-100;
Works in my case, if you run into the same problem like me and can't find a solution for that case and find this SO question.
Sorry for little bit off-topic, but as i just found out that this works, i thought it might be worth sharing.
Don't know if it is a dirty workaround, or actually legit.
Solution 19 - Javascript
You may use like this:
var num1 = '20',
num2 = '30.5';
alert((num1*1) + (num2*1)); //result 50.5
When apply *1 in num1, convert string a number.
if num1 contains a letter or a comma, returns NaN multiplying by 1
if num1 is null, num1 returns 0
kind regards!!!
Solution 20 - Javascript
Try this if you are looking for simple Javascript code and want to use two input box and add numbers from the two value. Here's the code.
Enter the first number: <input type="text" id="num1" /><br />
Enter the seccond number: <input type="text" id="num2" /><br />
<input type="button" onclick="call()" value="Add"/>
<script type="text/javascript">
function call(){
var q=parseInt(document.getElementById("num1").value);
var w=parseInt(document.getElementById("num2").value);
var result=q+w;
}
</script>
for more details please visit http://informativejavascript.blogspot.nl/2012/12/javascript-basics.html