Working with strings and numbers

- Now that we have operators to work with, let's look at how they interact with numbers and strings. In the previous examples, I used simple numbers to perform simple math operations. Var a equals four, var b equals five, var sum equals a plus b. That works fine as long as both parts of the equation is a number. But what happens when that's not the case? Take the following example. Var a still equals four, but var b is now the string five.

And var sum is still a plus b. Now, because one of the variables contains a string, javascript assumes you want to combine the two strings together and the plus symbol no longer works as an arithmetic operator, but as a string operator. The result we get is the string four five, or 45 which is the first variable followed by the second variable. Not at all four plus five. This is how we string different types of data together using javascript.

Using the plus symbol as a string operator, we add different content together to be treated as one long string. Any item included in such a string is treated like a string so a number will be converted to a string in this new context. The plus operator is unique in this regard. It's the only one of the arithmetic operators that is also a string operator, meaning you have to be careful about what type of data your variables contain when you use it.

If we use one of the other operators, say a minus b instead, the math works even though we have a number and a string. Javascript says you're trying to do math here and even though b is a string, I see it only contains a number so I'm going to assume you meant to use it as a number. The same thing happens when we do multiplication and division, as long as your string only contains a number, the math will work. It's sloppy and programmatically wrong, but you get results.

However, if you put anything other than a number in the string you're trying to subtract, multiply, or divide, bad things happen. If a is a number and b is a string and I try to say sum a minus b, then it returns NAN, or not a number. This means you're trying to do math using values that are not numbers, so if you ever seen NAN in your console, you know one or more of your variables contains a string.