run[If] and apply are functions that can help you craft easy-to-read code.
run forwards the first argument to the callback, and returns the result.
// Calculate the area.
const area = run(
getSize(),
({ width, height }) => width * height
);width and height are neatly confined to the callback. The alternative without run has those variables overstay their welcome, polluting the scope:
// Calculate the area.
const { width, height } = getSize();
const area = width * height;apply forwards the first argument to the callback ‒ just like run does ‒ but returns that argument instead of the result.
// Remove the item from the selection.
setState(previousSelection => apply(
new Set(previousSelection),
selection => selection.delete(item)
));The alternative without apply is more wordy:
// Remove the item from the selection.
setState(previousSelection => {
const selection = new Set(previousSelection);
selection.delete(item);
return selection;
});runIf skips the callback if the first argument is nullish, and behaves the same as run otherwise. runIf is to run as the ?. operator is to the . operator.
// Parse the timestamp (if any).
const timestamp = runIf(
response.data.timestamp,
Date.parse
);Alternatives include this:
// Parse the timestamp (if any).
let { timestamp } = response.data;
if (timestamp != undefined) {
timestamp = Date.parse(timestamp);
}And this*:
// Parse the timestamp (if any).
let timestamp = Date.parse(response.data.timestamp);
if (isNaN(timestamp)) {
timestamp = undefined;
}And this dangerous** one:
// Parse the timestamp (if any).
const timestamp = response.data.timestamp
&& Date.parse(response.data.timestamp);[*] In the alternative with isNaN, invalid timestamps (such as 'invalid') are indistinguishable from missing timestamps. This is likely unexpected behaviour.
[**] In the alternative with the && operator, Date.parse is skipped not only if the timestamp is undefined but also if it is '' (or any other falsy value). This too is likely unexpected.
You can combine runIf and the ?? operator to provide a fallback used if the callback is skipped.
return runIf(event.data, JSON.parse) ?? {};Install ruply using npm or Yarn and import the functions:
import { run, apply, runIf } from 'ruply';These are simplified implementations of run[If] and apply (without support for promises or chains):
function run(value, callback) {
return callback(value);
}
function apply(value, callback) {
callback(value);
return value;
}
function runIf(value, callback) {
return value != null ? callback(value) : value;
}These functions are designed to help your code better convey your intentions to the reader.
Non-goals include:
- producing the shortest possible code, and
- producing clever code.
Use run[If] and apply in situations where you feel they help the reader of your code.
let available = 0;
function generateID() {
return available++;
}run scopes the variable, protecting it from accidental access.
const generateID = run(0, available => () => available++);logger.log(`Received ${bundles.reduce(
(sum, { messages }) => sum + messages.length, 0
)} message(s)`);run moves the summing logic outside the template literal.
run(
bundles.reduce(
(sum, { messages }) => sum + messages.length, 0
),
messageCount =>
logger.log(`Received ${messageCount} message(s)`)
);if (data.has(index)) {
return data.get(index);
}
// If the buffer does not exist, allocate it…
const buffer = Buffer.alloc(size);
// …and store it in the map.
data.set(index, buffer);
return buffer;apply rearranges the pieces, producing code closer to human speech.
return data.get(index)
?? apply(
// If the buffer does not exist, allocate it…
Buffer.alloc(size),
// …and store it in the map.
buffer => data.set(index, buffer)
);const start = performance.now();
const result = await queryDatabase();
console.log(`${performance.now() - start} ms`);
return result;apply removes the need for the short-lived variable, and places return and queryDatabase() closer together.
const start = performance.now();
return apply(
queryDatabase(),
() => console.log(`${performance.now() - start} ms`)
);The await keyword is optional, as apply is promise-aware.
const token =
request.headers.authorization != undefined
? /^Bearer\s+(.*)$/.exec(
request.headers.authorization
)?.[1]
: undefined;runIf cuts out the undefined check (for cases where the header is missing) as well as the ?. operator (for cases where the regular expression does not match).
const token = runIf(
request.headers.authorization,
headerValue => /^Bearer\s+(.*)$/.exec(headerValue),
([, token]) => token
);If you prefer keeping the ?. operator, then you should.
const token = runIf(
request.headers.authorization,
headerValue => /^Bearer\s+(.*)$/.exec(headerValue)
)?.[1];const value = await cache.get(key);
// Disregard the value if it has expired.
if (value == null || value.expiration < Date.now()) {
return null;
}
return value;runIf cuts out the null check.
return runIf(
cache.get(key),
// Disregard the value if it has expired.
value => value.expiration < Date.now() ? null : value
);The await keyword is optional, as runIf is promise-aware.
const orders = new Map();
function memoGetOrder(id) {
if (orders.has(id)) {
return orders.get(id);
}
const order = getOrder(id);
orders.set(id, order);
return order;
}run scopes the map, while apply rearranges the pieces of the function body to match the human speech equivalent.
const memoGetOrder = run(new Map(), orders =>
id => orders.get(id)
?? apply(getOrder(id), order => orders.set(id, order))
);/ɹʌˈplaɪ/
Like run apply.
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