| Pipelines | \nTemporary Variables | \n\n\n\n
|---|---|
| \n\n```js\nconst envVarFormat = vars =>\n Object.keys(vars)\n .map(var => `${var}=${vars[var]}`)\n .join(' ')\n |> chalk.dim(%, 'node', args.join(' '));\n```\n\n | \n\n\n```js\nconst envVarFormat = (vars) => {\n let _ = Object.keys(vars);\n _ = _.map(var => `${var}=${vars[var]}`);\n _ = _.join(' ');\n return chalk.dim(_, 'node', args.join(' '));\n}\n```\n\n | \n
\n\n```jsx\n// This example uses JSX.\nreturn (\n
| \n\n\n```js\n// This example uses JSX.\nlet _ = values;\n_= Object.keys(_);\n_= [...Array.from(new Set(_))];\n_= _.map(envar => (\n
| \n
% is not a final choice\ntitle: ES pipe operator (2021)\nstatus: proposal\nstage: 2\nlocation: https://github.com/tc39/proposal-pipeline-operator\ncopyright: false\ncontributors: J. S. Choi, James DiGioia, Ron Buckton, Tab Atkins-Bittner\n\n\n\n\n
This is the formal specification for a proposed Hack-style pipe\n operator `|>` in JavaScript. It modifies the original
This document presumptively uses `%` as the token\n for the topic reference. This choice of token is not a final decision;\n `%` could instead be `^` or some other token.
\nThis section augments the
It presumptively uses `%` as the placeholder token for the\n topic reference. This choice of token is not a final decision; `%`\n could instead be `^` or some other token.
\nThis section augments the
It presumptively uses `%` as the placeholder token for the\n topic reference. This choice of token is not a final decision; `%`\n could instead be `^` or some other token.
\nThis section is a wholly new sub-clause of the
Several early error rules for |ScriptBody| and for\n |ModuleItemList|, as well as a step in CreateDynamicFunction,\n use the ContainsOuterTopic operation to check for any unbound topic reference `%`.\n Any inner topic reference within a |PipeBody| is hidden from these rules,\n preventing them from triggering the rules during program\n compilation.
\n\nThis guarantees that any topic reference in a program must be\n present within a topic-binding environment\n created by a |PipeBody| within that program.
\nEvery grammar production alternative in this specification which is not listed below implicitly has the following default definition of ContainsOuterTopic:
\n\nThis section augments the
It presumptively uses `%` as the placeholder token for the\n topic reference. This choice of token is not a final decision; `%`\n could instead be `^` or some other token.
\nThis section augments the
| Method | \nPurpose | \n
|---|---|
| Determine whether an Environment Record is a\n topic-binding environment. Return *true* if it establishes a\n topic binding and *false* if it does not. | \n
This section augments the
It presumptively uses `%` as the placeholder token for the\n topic reference. This choice of token is not a final decision; `%`\n could instead be `^` or some other token.
\nDeclarative Environment Records have the additional state fields\n listed in
| Method | \nValue | \nPurpose | \n
|---|---|---|
| [[TopicValues]] | \nList of any | \nIf the declarative Environment Record is a topic-binding\n environment, then [[TopicValues]] is a List containing the one element\n which is the environment's topic value (that is, the value of\n the topic reference within its program scope).\n Otherwise, the value of [[TopicValues]] is an empty List. | \n
[[TopicValues]] is a List in order to be forward compatible with\n future extensions that would use more than one topic value, e.g.,
Declarative Environment Records support all of the abstract methods\n of Environment Records listed in
| Method | \nPurpose | \n
|---|---|
| BindTopicValues(V) | \nEstablish the immutable topic binding of this\n Environment Record and set the topic binding's value.\n _V_ is a List containing the one element which is the\n topic value and is a value of any ECMAScript language\n type. Afterward, the Environment Record is a\n topic-binding environment, and the value returned by the\n Environment Record's HasTopicBinding method is *true*.\n This method cannot be called more than once on any\n single Environment Record. | \n
BindTopicValues accepts a List argument rather than a single-value\n argument in order to be forward compatible with future extensions that\n would use more than one topic value, e.g.,
The behaviour of the concrete and additional specification\n methods for declarative Environment Records is defined by the following\n algorithms.
\n\nThis section is a wholly new sub-clause of the
The concrete Environment Record method HasTopicBinding for\n declarative Environment Records returns whether the Environment Record\n is a topic-binding environment. The value is *true* only if its\n BindTopicValues method has been called.
\nThis section is a wholly new sub-clause of the
The method BindTopicValues for declarative Environment Records may\n only be called on an Environment Record when it is not yet a\n topic-binding environment, after which it does become a topic-binding\n environment.
\nThis section is a wholly new sub-clause of the
An Object Environment Record may never have a topic binding.
\nThis section is a wholly new sub-clause of the
A Global Environment Record may never have a topic binding.
\nThis section is a wholly new sub-clause of the
It presumptively uses `%` as the placeholder token for the\n topic reference. This choice of token is not a final decision; `%`\n could instead be `^` or some other token.
\nThe topic binding of a declarative Environment Record\n immutably binds the topic reference `%` to one value of any\n ECMAScript language type (called the topic value or simply\n the topic), within that declarative Environment Record, at\n the time of the Environment Record's instantiation. The topic of a\n declarative Environment Record conceptually serves as the value that its\n lexical context is \"about\".
\n\nA topic-binding environment is a declarative Environment\n Record that establishes a topic binding.\n The topic environment of the running execution context is its\n LexicalEnvironment's innermost Environment Record that is also a\n topic-binding environment (or *null* if no such Environment Record\n exists), as defined by the abstract operator GetTopicEnvironment.
\n\nAn Environment Record is a topic-binding environment\n only when it is a declarative Environment Record that\n was created by a |PipeBody|.
\nThis section augments the
EvaluateWithTopics creates a new topic-binding environment and\n evaluates the given _expression_ with that as its topic environment.\n The previous Lexical Environment is restored afterward.
\nGetTopicEnvironment returns the running execution context's topic environment\n (i.e., its LexicalEnvironment's innermost topic-binding environment)\n or *null* if the running execution context has no topic binding.
\nGetPrimaryTopicValue returns the topic value\n of the running execution context's topic environment.\n It may be called only when the running execution context's topic environment\n is not *null*.
\nThis section augments the
It presumptively uses `%` as the placeholder token for the\n topic reference. This choice of token is not a final decision; `%`\n could instead be `^` or some other token.
\nThis section augments the
It presumptively uses `%` as the placeholder token for the\n topic reference. This choice of token is not a final decision; `%`\n could instead be `^` or some other token.
\nThis section is a wholly new sub-clause to be inserted between the
It presumptively uses `%` as the placeholder token for the\n topic reference. This choice of token is not a final decision; `%`\n could instead be `^` or some other token.
\nThe topic reference, which is the token `%`, is a\n nullary operator that evaluates to the current Environment Record's\n topic value. The topic reference acts as if it were a special variable,\n implicitly bound to the topic value, yet still lexically scoped. But\n `%` is not actually an |IdentifierName| and the topic reference is\n not a variable, and it cannot be bound by typical assignment.\n Instead, the topic reference is immutably bound to a value\n during the instantiation of any topic-binding environment by a |PipeBody|.
\n\nThe concept of the topic binding is further discussed in
An unbound topic reference is a topic reference that\n is not present within any topic-binding environment created by a |PipeBody|.\n All unbound topic references are invalid syntax.\n Several early error rules for |ScriptBody| and for\n |ModuleItemList|, as well as a step in CreateDynamicFunction,\n use ContainsOuterTopic to check for any unbound topic reference `%`.\n Any inner topic reference within a |PipeBody| is hidden from these rules,\n preventing them from triggering the rules during program\n compilation.
\n\nThis guarantees that every topic reference in a program must be\n present within a topic-binding environment\n created by a |PipeBody| within that program.
\nA topic reference may be evaluated only when\n the running execution context's topic environment is not *null*.\n This is syntactically enforced by early error rules\n for |ScriptBody| and for |ModuleItemList|,\n as well as a step in CreateDynamicFunction.\n These rules use ContainsOuterTopic to check for any unbound topic reference.
\nThis section is a wholly new sub-clause to be inserted between the
This section is a wholly new sub-clause.
\n\nIt presumptively uses `%` as the placeholder token for the\n topic reference. This choice of token is not a final decision; `%`\n could instead be `^` or some other token.
\nA |PipeBody| must use its topic at least once.\n `value |> foo + 1` is an early error,\n because ContainsOuterTopic of its |PipeBody| is *false*.\n This design is such because omission of any topic reference from a |PipeBody|\n is almost certainly an accidental programmer error.
\nA |PipeBody| must not be an unparenthesized |AssignmentExpression|, such as |YieldExpression|, |ArrowFunction|, or |ConditionalExpression|—unless it is a |ShortCircuitExpression|.
\nThis is to prevent confusing expressions from being valid, such as:
\n\n x |> yield % |> % + 1 // Syntax Error\n This expression would otherwise be equivalent to:
\n\n x |> (yield % |> % + 1)\n Likewise, this expression:
\n\n x |> y ? % : z |> % + 1 // Syntax Error\n …would otherwise be equivalent to:
\n\n x |> (y ? % : z |> % + 1)\n These expressions are visually unclear and are therefore made invalid. The developer may make them valid with explicit parentheses:
\n\n x |> (yield %) |> % + 1\n x |> (yield % |> % + 1)\n x |> (y ? % : z) |> % + 1\n x |> (y ? % : z |> % + 1)\n This section augments the
It presumptively uses `%` as the placeholder token for the\n topic reference. This choice of token is not a final decision; `%`\n could instead be `^` or some other token.
\nAn early error rule uses ContainsOuterTopic\n to check for any unbound topic reference.\n Any inner topic reference within a |PipeBody| is hidden from this rule,\n preventing them from triggering the rule during program\n compilation.
\n\nThis guarantees that every topic reference in a |Script| must be\n present within a topic-binding environment created\n by a |PipeBody| within that |Script|.
\nThis section augments the
It presumptively uses `%` as the placeholder token for the\n topic reference. This choice of token is not a final decision; `%`\n could instead be `^` or some other token.
\nAn early error rule uses ContainsOuterTopic\n to check for any unbound topic reference.\n Any inner topic reference within a |PipeBody| is hidden from this rule,\n preventing them from triggering the rule during program\n compilation.
\n\nThis guarantees that every topic reference in a |ModuleBody| must be\n present within a topic-binding environment created\n by a |PipeBody| within that |ModuleBody|.
\nThis section augments the
It presumptively uses `%` as the placeholder token for the\n topic reference. This choice of token is not a final decision; `%`\n could instead be `^` or some other token.
\n