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JavaScript

Colin Grubbs
Colin Grubbs
2,137 Points
Posted by Colin Grubbs
Colin Grubbs
2,137 Points

isNaN question

I understand in the teacher notes below when he puts "if (isNan(lowNumber) || isNaN(highNumber))" to see if they are numbers.

However, in the video, he just puts "if (lowNumber && highNumber)". I understand that if the the statement in the parenthesis comes out to be true, then the first block runs. But lowNumber doesn't really have a "question" that can be resolved to true. It's just a variable right?

I'm guessing it has something to do with the line: lowNumber = parseFloat(lowNumber) that allows this to work.

2 Answers

John Johnson
John Johnson
11,790 Points
John Johnson
John Johnson
11,790 Points

If you just put the variable name in parenthesis, it will evaluate true if the variable is defined.

Colin Grubbs
Colin Grubbs
2,137 Points
Colin Grubbs
Colin Grubbs
2,137 Points

I see what you're saying. I am going to explain it in length to help myself and others who may not understand.

So basically, as long as lowNumber is defined, it will be true. Otherwise, it will be falsy. When we do parseFloat(lowNumber), the input that the user provides (for example, 6), is a string, but then gets changed to a number. If the user provides something like the number "6", then the input is able to get converted, and therefore has a value of 6 as a number. however, if the user inputs a non-numerical string, say, "dog", the parseFloat(lowNumber) will return NaN and therefore will come out as False in the "if" boolean context. So essentially, the parseFloat() is able to do the job of converting the input to a number as well as checking to see if the input is even a number (because it will be NaN if it is not a number). Therefore, you don't even have to use the isNaN() function in the "if" statement (but you can if you want).