util.js

Jump To … +

src/tuple.js src/universal-weak-map.js src/util.js

util.js
¶

Although Symbol is widely supported these days, we can safely fall back to using a non-enumerable string property without violating any assumptions elsewhere in the implementation.
```
const useSymbol = typeof Symbol === "function";
```
¶

Used to mark tuple.prototype so that all objects that inherit from any tuple.prototype object (there could be more than one) will test positive according to tuple.isTuple.
```
export const brand = useSymbol
  ? Symbol.for("immutable-tuple")
  : "@@__IMMUTABLE_TUPLE__@@";
```

Used to save a reference to the globally shared UniversalWeakMap that stores all known tuple objects.

export const globalKey = useSymbol
  ? Symbol.for("immutable-tuple-root")
  : "@@__IMMUTABLE_TUPLE_ROOT__@@";

The mustConvertThisToArray value is true when the corresponding Array method does not attempt to modify this, which means we can pass a tuple object as this without first converting it to an Array.

export function forEachArrayMethod(fn) {
  function call(name, mustConvertThisToArray) {
    const desc = Object.getOwnPropertyDescriptor(Array.prototype, name);
    fn(name, desc, !! mustConvertThisToArray);
  }

  call("every");
  call("filter");
  call("find");
  call("findIndex");
  call("forEach");
  call("includes");
  call("indexOf");
  call("join");
  call("lastIndexOf");
  call("map");
  call("reduce");
  call("reduceRight");
  call("slice");
  call("some");
  call("toLocaleString");
  call("toString");

¶

The reverse and sort methods are usually destructive, but for tuple objects they return a new tuple object that has been appropriately reversed/sorted.
```
  call("reverse", true);
  call("sort", true);
```

Make [...someTuple] work.

  call(useSymbol && Symbol.iterator || "@@iterator");
}