Why does it show value 5150 and not 155?

Question

So im quite new to javascript and i tried making something simple as entering a value and add 150 to it but it wont show number + 150? Pictures below

Dont mind the "check if your right" button, i was just messing around before i decided to make this — Philip Svenningsen Arnevig, Mar 29 '18 at 23:22

Javier S · Answer 1 · 2018-03-30T19:15:43.500

0

Because you're actually concatenating a string with a number. The input value is a string, so before operating with it, parse it to int with parseInt

edited Mar 30 '18 at 19:15

answered Mar 29 '18 at 23:24

Javier S

Thank you, i read through the link and it gave me a clearer picture :) – Philip Svenningsen Arnevig Mar 29 '18 at 23:31

score 0 · Accepted Answer · answered Mar 29 '18 at 23:24

0

That's because you are concatenating strings. You need to convert the strings to integers by using parseInt(), and then add the numbers.

var fullprice = parseInt(price) + 150;

answered Mar 29 '18 at 23:24

Gregory R.

Thank you very much, it worked! But i do wonder why it doesnt work with just price + 150 cause none of them are string or am i wrong? :) – Philip Svenningsen Arnevig Mar 29 '18 at 23:30
Yes, price is a string since you are using getElementById("pris").value to retrieve the value from HTML. – Gregory R. Mar 29 '18 at 23:35
Even thought there is no need to use types in Javascript, there are! An input can contain a number but it's value is returned as a String. `typeof "5"` would return `string` and `typeof 5` would return `number` – Javier S Mar 29 '18 at 23:37
Ah i see, so i would just use parseInt() to get number instead of string? :) – Philip Svenningsen Arnevig Mar 29 '18 at 23:40
Yes. you can always check the type of a variable by using the `typeof` operator. https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/typeof – Gregory R. Mar 29 '18 at 23:42
I see, thank you very much! – Philip Svenningsen Arnevig Mar 29 '18 at 23:49

2 Answers2