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NS-Proto-Appendix.md

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Record namespace

Record(obj: Object) -> Record

Converts shallowly an object to a record. If the object has a non-const value, a TypeError will be thrown.

Record.fromEntries(iterator: Iterator): Record

Similar to Object.fromEntries, but created a new Record.

Record[Symbol.hasInstance](v: unknown)

Returns true iff v is an object created by coercing a record primitive to an object via ToObject.

Tuple namespace

Tuple.from(arrayLike, mapFn, thisArg) => Tuple

Creates a shallow-copied Tuple from an array-like, iterable object, or another Tuple.

Optionally, a mapFn can be specified, which will be invoked for every value in arrayLike. The resulting Tuple will contain the return values of mapFn, rather than the original values. An optional thisArg can be specified, which will be used as the this value when invoking mapFn.

Tuple.from([1, 2, 3]); // #[1, 2, 3]
Tuple.from(#[1, 2, 3]); // #[1, 2, 3]

const set = new Set([1, 2, 3]);
set.add(0);
Tuple.from(set) // #[1, 2, 3, 0]

Tuple.of(values...) => Tuple

Creates a Tuple from a variable number of arguments, regardless of the number or types of the arguments.

Tuple.of(1,2,3); // #[1, 2, 3]

Tuple prototype

Tuple.prototype.toReversed()

Returns a Tuple of the same values as the original Tuple in reverse order.

Tuple.prototype.toSorted(compareFunction?)

Returns a Tuple of the same values as the original Tuple in sorted order. Optionally a compareFunction can be specified, otherwise the default sort order is to convert all values to strings, and comparing their sequences of UTF-16 code unit values.

Tuple.prototype.toSpliced(start, deleteCount?, items...)

Returns a new Tuple for which the elements are removed, replaced, or added to, removing deleteCount elements from index start, and inserting dding items starting at start.

Tuple.prototype.concat(values...)

Returns a new Tuple where the elements in the original Tuple are concatenated with the Tuples and values in values...;

Tuple.prototype.includes(valueToFind, fromIndex?)

Returns a boolean indicating whether valueToFind is an element of the Tuple. Optionally, fromIndex can be specified to specify an index into the Tuple to start searching for positive values, and tuple.length + fromIndex for negative values.

Tuple.prototype.indexOf(valueToFind, fromIndex?)

Returns the first index where the element is equal to valueToFind. Optionally, fromIndex can be specified to specify an index into the Tuple to start searching for positive values, and tuple.length + fromIndex for negative values. Returns -1 if valueToFind was not found in the Tuple.

Tuple.prototype.join(separator?)

Returns a string of the concatenated elements of the Tuple, separated by commas (by default) or the specified separator.

Tuple.prototype.lastIndexOf(valueToFind, fromIndex?)

Returns the last index where the element is equal to valueToFind. Optionally, fromIndex can be specified to specify an index into the Tuple to start searching for positive values, and tuple.length + fromIndex for negative values. Returns -1 if valueToFind was not found in the Tuple.

Tuple.prototype.slice(start, end?)

Returns a new Tuple containing the elements from the original Tuple starting at start and optionally ending at end exclusive.

Tuple.prototype.toString()

Returns a string containing the elements joined, and separated commas.

Tuple.prototype.toLocaleString(locales, options?)

Returns a string containing the elements joined, and separated by a locale-specific String. The elements are converted to strings via their toLocaleString methods. Where locales is a string or array of strings, and options is an object of configuration options.

Tuple.prototype.entries()

Returns a new Tuple iterator object that contains the key/value pairs for each index in the tuple.

Tuple.prototype.every(callback, thisArg?)

callback = function(element, index, tuple) { ... }

Returns true if the callback returns a truthy value for every element of the Tuple, otherwise false. Always returns true for empty Tuples. Optionally, thisArg can be specified, which will be used as the callback's this value.

Tuple.prototype.filter(callback, thisArg?)

callback = function(element, index, tuple) { ... }

Returns a new Tuple that contains the elements from the original Tuple for which callback returned a truthy value. Optionally, thisArg can be specified, which will be used as the callback's this value.

Tuple.prototype.find(callback, thisArg?)

callback = function(element, index, tuple) { ... }

Returns the value of the first element in the Tuple for which the callback returns a truthy value. Optionally, thisArg can be specified, which will be used as the callback's this value.

Tuple.prototype.findIndex(callback, thisArg?)

callback = function(element, index, tuple) { ... }

Returns the index of the first element in the Tuple for which the callback returns a truthy value, otherwise returns -1. Optionally, thisArg can be specified, which will be used as the callback's this value.

Tuple.prototype.forEach(callback, thisArg?)

callback = function(element, index, tuple) { ... }

Calls callback for each element in the Tuple in ascending order. Optionally, thisArg can be specified, which will be used as the callback's this value.

Tuple.prototype.keys()

Returns a Tuple Iterator object that contains the keys for each index in the Tuple.

Tuple.prototype.map(callback, thisArg?)

callback = function(element, index, tuple) { ... }

Returns a Tuple of the results of calling callback for each element. Optionally, thisArg can be specified, which will be used as the callback's this value.

Tuple.prototype.reduce(callback, initialValue?)

callback = function(accumulator, element, index, tuple) { ... }

Calls the reducer function callback on each element in the Tuple, resulting in a single value.

In the first call to callback, accumulator is the initialValue if provided, or the first value in the Tuple. Additionally, currentValue is the first value in the Tuple if initialValue is provided, the second value in the Tuple otherwise.

In subsequent calls, the accumulator is the return value of the previous call to callback.

If the Tuple is empty and no initialValue was provided, a TypeError is thrown.

If the Tuple has only one element and no initialValue was provided, the element is returned, without invoking callback.

If the Tuple has no elements and an initialValue was provided, the initialValue is returned, without invoking callback.

Tuple.prototype.reduceRight(callback, initialValue?)

callback = function(accumulator, element, index, tuple) { ... }

Calls the reducer function callback on each element in the Tuple, resulting in a single value.

Effectively the same as Tuple.prototype.reduce except right-to-left instead of left-to-right.

Tuple.prototype.some(callback, thisArg?)

callback = function(element, index, tuple) { ... }

Returns true if the callback returns a truthy value for at least one element of the Tuple, otherwise false. Always returns false for empty Tuples. Optionally, thisArg can be specified, which will be used as the callback's this value.

Tuple.prototype.values()

Returns a Tuple Iterator object that contains the values for each index in the Tuple.

Tuple.prototype[@@iterator]

Returns a Tuple Iterator object that contains the values for each index in the Tuple.

Tuple.prototype.with(index, value)

Returns a Tuple with the same elements as the original Tuple except the element at index is replaced with value.

Compatibility with the existing Object methods

NOTE: Since Record doesn't inherit from Object, you can't directly call the Object.prototype.* methods but you have to use .call().

Object methods which work with Record and Tuple

  • Object.is() - When comparing records and tuples it behaves exactly like ===

  • Object.entries(), Object.keys(), Object.values() - The resulting arrays are sorted alphabetically by key

  • Object.assign() - Copy properties from a record or tuple to another object. Caveat: The first argument cannot be a record or a tuple, because they are immutable

  • Object.isExtensible(), Object.isFrozen(), Object.isSealed() - When called on records and tuples, they always return false, true, and true respectively

  • Object.preventExtension(), Object.freeze(), Object.seal() - Records and tuples are already immutable, so these methods will not throw but won't have any effect

  • Object.getOwnPropertyDescriptor(), Object.getOwnPropertyDescriptors() - The resulting descriptors all have writable: false, enumerable: true, configurable: false

  • Object.getOwnPropertyNames(), Object.getOwnPropertySymbols(), Object.getPrototypeOf() - Behave similarly to when called on objects

  • Object.prototype.toString, Object.prototype.toLocaleString - Return [object Record] and [object Tuple] when a Record or Tuple is the receiver

  • Object.prototype.valueOf - Boxes a primitive record or tuple into an object

  • Object.prototype.propertyIsEnumerable - Always returns true for existing properties

  • Object.prototype.hasOwnProperty

  • Object.prototype.isPrototypeOf

Object methods which don't work with Record and Tuple

  • Object.create() - Records and tuples cannot be used as prototypes, unless you wrap them in objects (Object(#{}))
  • Object.defineProperties(), Object.defineProperty(), Object.setPrototypeOf() - Records and tuples are immutable by design.