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javascriptjqueryincrement
Wang Dang
Wang Dang

Reputation: 131

JavaScript/jQuery: Why is my increment not working?

I have two buttons and there is a form in between. One button says "+" and the other "-". I am trying to make increment/decrement buttons, but it is not properly working. It seems like addition is causing a problem where increment is not happening, and instead, concatenation is happening. For example, when the form value is 0, and "+" button is pressed, it changes the 0 to 01. My JavaScript code has 

//assume the oldValue read 0 from the form
newValue = oldValue + 1
alert(newValue); //this returns 01 instead of 1

When the oldValue is 01 and increment again, it returns 011. Why is this not incrementing, but concatenating the 1 at the end? Surprisingly, decrement is working perfectly with the same code except that I have a minus where there is a plus.

How can you increment a form value in peace? and can anyone explain why "+ 1" does not work?

Upvotes: 0

Views: 1062

Answers (3)

Justin
Justin

Reputation: 91

CASE 1:

var a=1;
var b=2;

alert(a+b);// RESULT WILL BE 3

CASE 2:

var a='1';
var b=2;

alert(a+b);// RESULT WILL BE 12

If you are getting values from a Form or something , your value will be treated as a string (like '1') . You can convert if to number/int by Using the Keyword Number , Like below

alert(Number(a)+b);

Upvotes: 1

Mayank Pandeyz
Mayank Pandeyz

Reputation: 26258

Try this:

newValue = parseInt(oldValue) + 1;

This is happening because oldValue datatype is string and when you add a Int to a String then the output is also a string. So you have to convert it into a number before adding some int value into it.

Upvotes: 1

almost a beginner
almost a beginner

Reputation: 1632

newValue = Number(oldValue) + 1

I think you forgot to convert string to int.

Upvotes: 1

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