Javascript increment operator

Question

totalvalue = 0;
for (x=1; x<6; x++)
{
totalvalue += document.getElementById("rcv_amount_"+x).value;
}

rcv_amount_1 = 2 rcv_amount_2 = 4 rcv_amount_3 = 6

expected result is 12, but i am getting 0246.

Any help?

• toniedzwiedz: You're adding strings, convert them to numbers and you'll be fine ;)
• Ende Neu: Looks like you're concatenating strings instead of making additions.

Answer 1

You have to convert the .value into a number - initially the .value property of an <input> element is a string, so the += operator results in concatenation, not addition.

To convert a string value into a number you can use parseInt(..., 10) for integers, or parseFloat(...) or just +(...) for non-integers.

Answer 2

Try with

totalvalue += parseInt(document.getElementById("rcv_amount_"+x).value, 10);

• ThiefMaster: You should always specify the second argument to parseInt, i.e. `parseInt(..., 10) to ensure the value is treated as a decimal number (and not e.g. octal or hex)
• makmonty: As far as I know, that parameters is optional, and 10 by default.
• ThiefMaster: No, by default it's guessed from the string. And while octal (leading zero) is gone in most browsers, it still handles 0x... as hex
• toniedzwiedz: Couln't agree more. Always use JSLint to prevent such situations. They can be a pain to find.
• Alnitak: @Portnoy it's optional, but the default value is zero, meaning "figure it out from the string".