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spec.emu
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<!DOCTYPE html>
<meta charset="utf8" />
<link rel="stylesheet" href="./spec.css" />
<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/highlight.js/8.4/styles/github.min.css" />
<script src="./spec.js"></script>
<pre class="metadata">
title: Range proposal
status: proposal
stage: 1
location: https://tc39.es/proposal-Number.range
copyright: false
contributors: Jack Works
</pre>
<emu-clause id="sec-control-abstraction-objects" number="27">
<h1>Control Abstraction Objects</h1>
<emu-clause id="sec-iteration" number="1">
<h1>Iteration</h1>
<emu-clause id="sec-iterator-objects" number="3">
<h1>Iterator Objects</h1>
<emu-clause id="sec-properties-of-the-iterator-constructor" number="2">
<h1>Properties of the Iterator Constructor</h1>
<emu-clause id="sec-iterator.range" number="2">
<h1>Iterator.range ( _start_, _end_, _optionOrStep_ )</h1>
<emu-alg>
1. If _start_ is a Number, return ? CreateNumericRangeIterator(_start_, _end_, _optionOrStep_, ~number-range~).
1. If _start_ is a BigInt, return ? CreateNumericRangeIterator(_start_, _end_, _optionOrStep_, ~bigint-range~).
1. Throw a *TypeError* exception.
</emu-alg>
</emu-clause>
</emu-clause>
</emu-clause>
<emu-clause id="sec-numeric-range-iterator-object">
<h1>The <dfn>NumericRangeIterator</dfn> Object</h1>
<p>A NumericRangeIterator object is an iterator that yields numbers. There is not a named constructor for NumericRangeIterator objects. Instead, NumericRangeIterator objects are created by the CreateNumericRangeIterator abstract operation as needed.</p>
<emu-clause id="sec-create-numeric-range-iterator" type="abstract operation">
<h1>
CreateNumericRangeIterator (
_start_: a Number or a BigInt,
_end_: an ECMAScript language value,
_optionOrStep_: an ECMAScript language value,
_type_: ~number-range~ or ~bigint-range~
) : either a normal completion containing an ECMAScript language value or a throw completion
</h1>
<dl class="header"></dl>
<emu-alg>
1. If _start_ is *NaN*, throw a *RangeError* exception.
1. If _end_ is *NaN*, throw a *RangeError* exception.
1. If _type_ is ~number-range~, then
1. Assert: _start_ is a Number.
1. If _end_ is not a Number, throw a *TypeError* exception.
1. Let _zero_ be *+0*<sub>𝔽</sub>.
1. Let _one_ be *1*<sub>𝔽</sub>.
1. Else,
1. Assert: _start_ is a BigInt.
<emu-note type="editor">Allowing all kinds of number (bigint, decimals, ...) to range from a finite number to infinity.</emu-note>
1. If _end_ is not *+∞*<sub>𝔽</sub> or *-∞*<sub>𝔽</sub> and _end_ is not a BigInt, throw a *TypeError* exception.
1. Let _zero_ be *0*<sub>ℤ</sub>.
1. Let _one_ be *1*<sub>ℤ</sub>.
1. If _start_ is *+∞*<sub>𝔽</sub> or *-∞*<sub>𝔽</sub>, throw a *RangeError* exception.
1. Let _inclusiveEnd_ be *false*.
1. If _optionOrStep_ is *undefined* or *null*, then
1. Let _step_ be *undefined*.
1. Else if _optionOrStep_ is an Object, then
1. Let _step_ be ? Get(_optionOrStep_, *"step"*).
1. Set _inclusiveEnd_ to ToBoolean(? Get(_optionOrStep_, *"inclusive"*)).
1. Else if _type_ is ~number-range~ and _optionOrStep_ is a Number, then
1. Let _step_ be _optionOrStep_.
1. Else if _type_ is ~bigint-range~ and _optionOrStep_ is a BigInt, then
1. Let _step_ be _optionOrStep_.
1. Else,
1. Throw a *TypeError* exception.
1. If _step_ is *undefined* or *null*, then
1. If _end_ is *+∞*<sub>𝔽</sub>, let _step_ be _one_.
1. Else if _end_ is *-∞*<sub>𝔽</sub>, let _step_ be -_one_.
1. Assert: In the next branch, _end_ is a BigInt and _start_ is a BigInt, or _end_ is a Number and _start_ is a Number.
1. Else if _end_ > _start_, let _step_ be _one_.
1. Else let _step_ be -_one_.
1. If _step_ is *NaN*, throw a *RangeError* exception.
1. If _type_ is ~number-range~ and _step_ is not a Number, throw a *TypeError* exception.
1. Else if _type_ is ~bigint-range~ and _step_ is not a BigInt, throw a *TypeError* exception.
1. If _step_ is *+∞*<sub>𝔽</sub> or *-∞*<sub>𝔽</sub>, throw a *RangeError* exception.
1. If _step_ is _zero_ and _start_ is not _end_, throw a *RangeError* exception.
1. Let _closure_ be a new Abstract Closure with no parameters that captures _start_, _end_, _step_, _inclusiveEnd_, _zero_, _one_ and performs the following steps when called:
1. If _end_ is *+∞*<sub>𝔽</sub>, let _ifIncrease_ be *true*.
1. Else if _end_ is *-∞*<sub>𝔽</sub>, let _ifIncrease_ be *false*.
1. Assert: In the next branch, _end_ is a BigInt and _start_ is a BigInt, or _end_ is a Number and _start_ is a Number.
1. Else if _end_ > _start_, let _ifIncrease_ be *true*.
1. Else let _ifIncrease_ be *false*.
1. If _step_ > _zero_, let _ifStepIncrease_ be *true*.
1. Else let _ifStepIncrease_ be *false*.
1. If _ifIncrease_ is not _ifStepIncrease_, return *undefined*.
1. Let _hitsEnd_ be *false*.
1. Let _currentCount_ be _zero_.
1. NOTE: You can debug these steps at https://tc39.es/proposal-Number.range/playground.html .
1. Repeat, while _hitsEnd_ is *false*,
1. Let _currentYieldingValue_ be _start_ + (_step_ \* _currentCount_).
1. If _currentYieldingValue_ is _end_, Set _hitsEnd_ to *true*.
1. Set _currentCount_ to _currentCount_ + _one_.
1. If _ifIncrease_ is *true*, then
1. Assert: _end_ is a BigInt or *+∞*<sub>𝔽</sub> and _currentYieldingValue_ is a BigInt, or _end_ is a Number and
_currentYieldingValue_ is a Number.
1. If _end_ is not *+∞*<sub>𝔽</sub>, then
1. If _inclusiveEnd_ is *true*, then
1. If _currentYieldingValue_ > _end_, return *undefined*.
1. Else,
1. If _currentYieldingValue_ ≥ _end_, return *undefined*.
1. Else,
1. Assert: _end_ is a BigInt or *-∞*<sub>𝔽</sub> and _currentYieldingValue_ is a BigInt, or _end_ is a Number and _currentYieldingValue_ is a Number.
1. If _end_ is not *-∞*<sub>𝔽</sub>, then
1. If _inclusiveEnd_ is *true*, then
1. If _end_ > _currentYieldingValue_, return *undefined*.
1. Else,
1. If _end_ ≥ _currentYieldingValue_, return *undefined*.
1. Perform ? Yield(_currentYieldingValue_).
1. Return *undefined*.
1. Return CreateIteratorFromClosure(_closure_, *"%NumericRangeIteratorPrototype%"*, %NumericRangeIteratorPrototype%).
</emu-alg>
</emu-clause>
<emu-clause id="sec-%numericrangeiteratorprototype%-object">
<h1>The %NumericRangeIteratorPrototype% Object</h1>
<p>The <dfn>%NumericRangeIteratorPrototype%</dfn> object:</p>
<ul>
<li>has properties that are inherited by all NumericRangeIterator Objects.</li>
<li>is an ordinary object.</li>
<li>has a [[Prototype]] internal slot whose value is %IteratorPrototype%.</li>
<li>has the following properties:</li>
</ul>
<emu-clause id="sec-properties-of-the-numericrangeiterator-prototype-object-next">
<h1>%NumericRangeIterator%.next ( )</h1>
<emu-alg>
1. Return ? GeneratorResume(*this* value, ~empty~, *"%NumericRangeIteratorPrototype%"*).
</emu-alg>
</emu-clause>
<emu-clause id="sec-properties-of-the-numericrangeiterator-prototype-object-@@tostringtag">
<h1>%NumericRangeIteratorPrototype%.[@@toStringTag]</h1>
<p>The initial value of the @@toStringTag property is the String value `"NumericRangeIterator"`.</p>
<p>This property has the attributes { [[Writable]]: *false*, [[Enumerable]]: *false*, [[Configurable]]: *true* }.</p>
</emu-clause>
</emu-clause>
</emu-clause>
</emu-clause>
</emu-clause>