How to enforce integer sizes in JS? (TypeScript?)

Question

I'm working on a JavaScript project that would benefit hugely from being able to have some very specific integer types enforced (uint8, int256, int20...). I was tempted to use TypeScript but the more I explore it seems to be a bit of misnomer.

I expect a number of responses along the lines of 'don't use JavaScript'. This is a JS implementation of a spec and thus must conform the to spec. I believe that by enforcing these types I can achieve more robust and readable code. I do wonder if someone can make an argument for why this would not be worth the benefits.

Answer 1

For typical machine bit-sizes, you could use typed arrays.

For example,

const typedArray1 = new Int8Array(8);
typedArray1[0] = 32;

This array will store 8-bit signed integers.

For each integer type, you have a corresponding typed array.

See MDN for more details.

For other bit-sizes, I do not have an easy solution.

Answer 2

Typescript allows numbers to be types, and those types can be combined with a type union:

 type uint8 = 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | 32 | 33 | 34 | 35 | 36 | 37 | 38 | 39 | 40 | 41 | 42 | 43 | 44 | 45 | 46 | 47 | 48 | 49 | 50 | 51 | 52 | 53 | 54 | 55 | 56 | 57 | 58 | 59 | 60 | 61 | 62 | 63 | 64 | 65 | 66 | 67 | 68 | 69 | 70 | 71 | 72 | 73 | 74 | 75 | 76 | 77 | 78 | 79 | 80 | 81 | 82 | 83 | 84 | 85 | 86 | 87 | 88 | 89 | 90 | 91 | 92 | 93 | 94 | 95 | 96 | 97 | 98 | 99 | 100 | 101 | 102 | 103 | 104 | 105 | 106 | 107 | 108 | 109 | 110 | 111 | 112 | 113 | 114 | 115 | 116 | 117 | 118 | 119 | 120 | 121 | 122 | 123 | 124 | 125 | 126 | 127 | 128 | 129 | 130 | 131 | 132 | 133 | 134 | 135 | 136 | 137 | 138 | 139 | 140 | 141 | 142 | 143 | 144 | 145 | 146 | 147 | 148 | 149 | 150 | 151 | 152 | 153 | 154 | 155 | 156 | 157 | 158 | 159 | 160 | 161 | 162 | 163 | 164 | 165 | 166 | 167 | 168 | 169 | 170 | 171 | 172 | 173 | 174 | 175 | 176 | 177 | 178 | 179 | 180 | 181 | 182 | 183 | 184 | 185 | 186 | 187 | 188 | 189 | 190 | 191 | 192 | 193 | 194 | 195 | 196 | 197 | 198 | 199 | 200 | 201 | 202 | 203 | 204 | 205 | 206 | 207 | 208 | 209 | 210 | 211 | 212 | 213 | 214 | 215 | 216 | 217 | 218 | 219 | 220 | 221 | 222 | 223 | 224 | 225 | 226 | 227 | 228 | 229 | 230 | 231 | 232 | 233 | 234 | 235 | 236 | 237 | 238 | 239 | 240 | 241 | 242 | 243 | 244 | 245 | 246 | 247 | 248 | 249 | 250 | 251 | 252 | 253 | 254;

  let works: uint8 = 5;

  let doesntWork: uint8 = 2000;

Now those types are only enforced at conpile time, to mitigate this you could use a function that performs a runtime check:

 function toUint(n: number): uint8 {
   if(!Number.isInteger(n) || n < 0 || n > 255) throw new RangeError("Number is out of Uint8 range");
   return n as uint8;
 }

 const works: uint8 = toUint(Math.random() * 100);

It might get better in the future, there is a proposal to support range types which will beautify the whole thing to:

 type uint8 = 0..255;

Answer 3

It is not possible with build-in types so just create a class wrapper with getter and setter for each of your types. Like this:

class Uint8 {
    private _value: number;

    get value(): number {
        return this._value;
    }

    set value(newValue: number) {
        if (newValue < 0 || newValue >255 || Math.round(newValue) !== newValue) return;
        this._value = newValue;
    }
}