Simple Javascript syntax behaving unexpectedly

Question

It is showing 60 + 5 as 605 instead of 65

g = document.getElementById("height1").value * 12;
alert(g);    <---- This is showing 60
h = document.getElementById("height2").value;
alert(h);   <---- This is showing 5
b = g+h;
alert(b);    <---- This is showing 605

Any ideas

score 3 · Answer 1 · answered Nov 04 '14 at 18:24

3

Use parseInt() to convert to integer. + in Javascript is both for adding and concatenation.

answered Nov 04 '14 at 18:24

EvilZebra

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score 3 · Accepted Answer · answered Nov 04 '14 at 18:24

3

Javacript is not a strongly typed language. It does it's best to interpret the type of variables and generally, if you try to add a string-like variable to an integer-like variable, it will interpret it as string concatenation.

You could force the variables to be interpreted as integers like this:

 b = parseInt(g) + parseInt(h);

Or, using other tricks that will force the variable to become numeric, like this:

 b = (g*1) + (h*1);

answered Nov 04 '14 at 18:24

Mike Dinescu

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Make sure to [always include the radix](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/parseInt#Parameters) when calling `parseInt()` – Dave Nov 07 '14 at 21:55

score 0 · Answer 3 · answered Nov 04 '14 at 18:23

0

how about b = (g+h)?

make sure the vars are integers, else convert them to integers

answered Nov 04 '14 at 18:23

Medda86

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ok then use b = parseInt(g)+parseInt(h) – Medda86 Nov 04 '14 at 18:26

score 0 · Answer 4 · answered Nov 04 '14 at 18:25

If the values of those HTML elements are strings (like in text input boxes?) then what you're doing is concatenating strings, not adding numbers.

You need to 1) be sure the input values are actually numeric, and 2) convert the string to an integer using parseInt().

Simple Javascript syntax behaving unexpectedly

4 Answers4