11/12 Explaining parseInt()

As the name suggests, the function parses an integer out of a string (or float) expression.

console.log(parseInt("1010", 2)); // binary to dec => 10
console.log(parseInt("A", 16)); // hexadecimal to dec => 10
console.log(parseInt("FF", 16)); // hexadecimal to dec => 255
console.log(parseInt("31", 8)); // octal to dec => 25

And we should toss in,

console.log(parseInt("42", 10)); // string dec to dec => 42

The second parameter is the radix or number base represented by the string. We can use this method to parse out the integral of a float, as earlier mentioned:

console.log(parseInt(Math.PI, 10)); // 3

JavaScript defaults to base 10 but best practice is to always include the radix in this expression.

key.which is pretty self-explanatory… Which key? key is the name we gave the transient KeyboardEvent Object in the parameter of the handler function. This lets us view all the properties of the event object, specifically the which property.

Tip: Since we are using the .keydown() method, this value will be uppercase ASCII for the letter keys if you wish to also incorporate a,s,w,d for the left hand.

Object data can be either string or number and still represent a number, as we’ve seen. Depending on the user agent, which might be a string, or it might be a number. parseInt() let’s us treat it as a number so it matches our case expressions, which are all numbers in this program.

I did my own study of the KeyboardEvent Object in Codebits. It only displays data and not methods. You might find it useful to examine. JavaScript is loaded with these kinds of objects, and this is a good one to understand.