You can also use the Unicode escape sequences as characters in identifiers. A variable declared using the var or let statement with no assigned value specified has the value of undefined. An attempt to access an undeclared variable will result in a ReferenceError exception being thrown:. You can use undefined to determine whether a variable has a value.
In the following code, the variable input is not assigned a value, and the if statement evaluates to true. The undefined value behaves as false when used in a boolean context.
For example, the following code executes the function myFunction because the myArray element is undefined:. When you evaluate a null variable, the null value behaves as 0 in numeric contexts and as false in boolean contexts. When you declare a variable outside of any function, it is called a global variable, because it is available to any other code in the current document. When you declare a variable within a function, it is called a local variable, because it is available only within that function.
All other commas in the list indicate a new element. Trailing commas can create errors in older browser versions and it is a best practice to remove them. In the following example, the length of the array is four, and myList and myList are missing.
Property names that are not valid identifiers also cannot be accessed as a dot. Together, these also bring object literals and class declarations closer together, and let object-based design benefit from some of the same conveniences.
You can also use the String. In ES, template literals are also available. Template strings provide syntactic sugar for constructing strings. This is similar to string interpolation features in Perl, Python and more.
A key characteristic of the genre is that the game world is procedurally generated and this one is no exception. In traditional roguelike spirit, there is no pre-rendered art.
Great, now I can just write a function which creates these tile objects and then store them all in a 2D array to represent the world…. But what happens when you want to generate a map the size of a planet?
The code for this experiment can be found in this gist. What happens when you need to add a new field though? Another number, push the boat out and go as far as a string? More bits, bigger formats, bad things all round. Now our height has decimal precision and that is more complicated to store than regular integers.
We need to decide on a limit and then simply store just that amount of precision instead. Effectively, we can get away with storing them as integers 0 to Finally our vegetation boolean only needs a single bit and that is all there is to say about that. However, 17 is a tricky number when it comes to storage. However, if we knew this was going to be the canonical format, we could shorten the first field by 1 bit and use 7 bits to represent tile types instead. Condensing the format to fit nicely into two bytes is an exercise left for the reader.
We could use an array of booleans, to store the individual bits in sequence, but then we put ourselves at the mercy of the implementation, not the specification. All that work for nothing…. We need to do a small amount of work to the height and vegetation properties, but afterwards, the underlying representation of these values looks like this.
If we reference our initial format design, we can check the field length for height. It was 8 bits. It simply moves the bit pattern left by how every many places you specify in the right hand side operand. Then we simply rinse and repeat, until we have all of our fields inside our packaged number. Quite simply, do the opposite.
The initial generation time could be faster, but the fault is with the diamond square implementation, not the tile format. To render the tiles, we use their height as the lightness value for a hsl colour to create the transition effects. Any tiles with the vegetation flag set, will also have a greenrendered above them. The Tile In this game, a tile is defined by its type earth, water, sand, rockits height between 0 and 1 and whether it contains any vegetation.