Add string to a number in Javascript

Question

I have function addNumber and if I click on button with specific value, the value is concatenate to variable b. But if the value of "a" is other than number, the function doesn't work. What am I missing? I thought that the function works with parameter "a" as if it was a string. Otherwise the number were add up. So if b=0, a=x; the result of b=b+a will be x.

function addNumber(a) {
    b=b+a;
    document.getElementById("result").innerHTML= b;
}

I think that problem is here.

function addNumber(a) {

document.getElementById("result").innerHTML= String(a);
}

If the parameter "a" is number, it returns number, but if the parameter "a" is equals some string, returns nothing. Why?

But what exactly you want. Answer these! 1. if b=10 and a=10 Result=20; 2. If b=0 and a=x Result=?? 3. b=a and a= s or ss..ssss.. etc., Result=?? — Padmanaban
– Padmanaban, Commented Aug 23, 2015 at 7:46

Mureinik · Accepted Answer · 2015-08-23 07:37:19Z

2

If you want to treat both variables as strings, you could explicitly cast them as such:

function addNumber(a) {
    b = String(b) + String(a);
    document.getElementById("result").innerHTML= b;
}

answered Aug 23, 2015 at 7:37

Mureinik

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2 Comments

trenccan Over a year ago

this works but what I want to do is concatenate 2 or more numbers. Im making calculator. If I click on button 1, result will be 1, if I click than on 2, the result will be 12. Now it is working but if I click for instance on comma sign, it doesn't return 12, .

Chihung Yu Over a year ago

Javascript is a loose type language, so nothing stop you from passing illegal types. Since you are making a calculator, you should check if the input is from 0~9 first, if it is then call addNumber if it's not then do something else.

ashishmaurya · Accepted Answer · 2015-08-23 07:39:23Z

1

If you want to add 2 numbers then you need to parse string into number before adding. parseInt is used for parsing string to integer.

If its not parsed then it will be treated as string and + will act as concatenation operator

answered Aug 23, 2015 at 7:39

ashishmaurya

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1 Comment

trenccan Over a year ago

Yes I understand. I want to concatenate numbers, but sometimes I want to concatenate number with string and the function above is working good when the a parameter represent number, but if it is a string, it doesn't concatenate the number and string together as I expected.

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