Performs left-to-right function composition for asynchronous functions.
Use Array.prototype.reduce() with the spread operator (...) to perform left-to-right function composition using Promise.then(). The functions can return a combination of: simple values, Promise's, or they can be defined as async ones returning through await. All functions must be unary.
const pipeAsyncFunctions = (...fns) => arg => fns.reduce((p, f) => p.then(f), Promise.resolve(arg)); -
const sum = pipeAsyncFunctions( +
+const sum = pipeAsyncFunctions( x => x + 1, x => new Promise(resolve => setTimeout(() => resolve(x + 2), 1000)), x => x + 3, async x => (await x) + 4 ); -(async () => { +(async() => { console.log(await sum(5)); // 15 (after one second) })();
Performs left-to-right function composition.
Use Array.prototype.reduce() with the spread operator (...) to perform left-to-right function composition. The first (leftmost) function can accept one or more arguments; the remaining functions must be unary.
const pipeFunctions = (...fns) => fns.reduce((f, g) => (...args) => g(f(...args))); diff --git a/docs/index.html b/docs/index.html index 202d4f792..05c919edc 100644 --- a/docs/index.html +++ b/docs/index.html @@ -403,12 +403,13 @@
Takes a predicate and array, like Array.prototype.filter(), but only keeps x if pred(x) === false.
const reject = (pred, array) => array.filter((...args) => !pred(...args));
reject(x => x % 2 === 0, [1, 2, 3, 4, 5]); // [1, 3, 5] reject(word => word.length > 4, ['Apple', 'Pear', 'Kiwi', 'Banana']); // ['Pear', 'Kiwi'] -
Removes elements from an array for which the given function returns false.
Use Array.prototype.filter() to find array elements that return truthy values and Array.prototype.reduce() to remove elements using Array.prototype.splice(). The func is invoked with three arguments (value, index, array).
const remove = (arr, func) => +
Removes elements from an array for which the given function returns false.
Use Array.prototype.filter() to find array elements that return truthy values and Array.prototype.reduce() to remove elements using Array.prototype.splice(). The func is invoked with three arguments (value, index, array).
+const remove = (arr, func) => Array.isArray(arr) ? arr.filter(func).reduce((acc, val) => { - arr.splice(arr.indexOf(val), 1); - return acc.concat(val); - }, []) + arr.splice(arr.indexOf(val), 1); + return acc.concat(val); + }, []) : [];
remove([1, 2, 3, 4], n => n % 2 === 0); // [2, 4]
Returns a random element from an array.
Use Math.random() to generate a random number, multiply it by length and round it off to the nearest whole number using Math.floor(). This method also works with strings.
const sample = arr => arr[Math.floor(Math.random() * arr.length)]; diff --git a/docs/math.html b/docs/math.html index eb33562eb..7d25685e1 100644 --- a/docs/math.html +++ b/docs/math.html @@ -147,11 +147,12 @@ For teams, each rating can adjusted based on own team's average rating vs. average rating of opposing team, with the score being added to their own individual rating by supplying it as the third argument. */ -
Calculates the factorial of a number.
Use recursion. If n is less than or equal to 1, return 1. Otherwise, return the product of n and the factorial of n - 1. Throws an exception if n is a negative number.
const factorial = n => +
Calculates the factorial of a number.
Use recursion. If n is less than or equal to 1, return 1. Otherwise, return the product of n and the factorial of n - 1. Throws an exception if n is a negative number.
+const factorial = n => n < 0 ? (() => { - throw new TypeError('Negative numbers are not allowed!'); - })() + throw new TypeError('Negative numbers are not allowed!'); + })() : n <= 1 ? 1 : n * factorial(n - 1); diff --git a/docs/object.html b/docs/object.html index 916164842..40d4fa12b 100644 --- a/docs/object.html +++ b/docs/object.html @@ -130,13 +130,14 @@ o[0[ 1][0] = 4; // not allowed as well
Assigns default values for all properties in an object that are undefined.
Use Object.assign() to create a new empty object and copy the original one to maintain key order, use Array.prototype.reverse() and the spread operator ... to combine the default values from left to right, finally use obj again to overwrite properties that originally had a value.
const defaults = (obj, ...defs) => Object.assign({}, obj, ...defs.reverse(), obj);
defaults({ a: 1 }, { b: 2 }, { b: 6 }, { a: 3 }); // { a: 1, b: 2 } -
Returns the target value in a nested JSON object, based on the given key.
Use the in operator to check if target exists in obj. If found, return the value of obj[target], otherwise use Object.values(obj) and Array.prototype.reduce() to recursively call dig on each nested object until the first matching key/value pair is found.
const dig = (obj, target) => +
Returns the target value in a nested JSON object, based on the given key.
Use the in operator to check if target exists in obj. If found, return the value of obj[target], otherwise use Object.values(obj) and Array.prototype.reduce() to recursively call dig on each nested object until the first matching key/value pair is found.
+const dig = (obj, target) => target in obj ? obj[target] : Object.values(obj).reduce((acc, val) => { - if (acc !== undefined) return acc; - if (typeof val === 'object') return dig(val, target); - }, undefined); + if (acc !== undefined) return acc; + if (typeof val === 'object') return dig(val, target); + }, undefined);
const data = { level1: { level2: { diff --git a/snippets/dig.md b/snippets/dig.md index c97559833..a349ef2d3 100644 --- a/snippets/dig.md +++ b/snippets/dig.md @@ -6,13 +6,14 @@ Use the `in` operator to check if `target` exists in `obj`. If found, return the value of `obj[target]`, otherwise use `Object.values(obj)` and `Array.prototype.reduce()` to recursively call `dig` on each nested object until the first matching key/value pair is found. ```js + const dig = (obj, target) => target in obj ? obj[target] : Object.values(obj).reduce((acc, val) => { - if (acc !== undefined) return acc; - if (typeof val === 'object') return dig(val, target); - }, undefined); + if (acc !== undefined) return acc; + if (typeof val === 'object') return dig(val, target); + }, undefined); ``` ```js diff --git a/snippets/factorial.md b/snippets/factorial.md index 86ebe69b6..2266247b4 100644 --- a/snippets/factorial.md +++ b/snippets/factorial.md @@ -8,11 +8,12 @@ Otherwise, return the product of `n` and the factorial of `n - 1`. Throws an exception if `n` is a negative number. ```js + const factorial = n => n < 0 ? (() => { - throw new TypeError('Negative numbers are not allowed!'); - })() + throw new TypeError('Negative numbers are not allowed!'); + })() : n <= 1 ? 1 : n * factorial(n - 1); diff --git a/snippets/pipeAsyncFunctions.md b/snippets/pipeAsyncFunctions.md index 8c93add3b..61b850a39 100644 --- a/snippets/pipeAsyncFunctions.md +++ b/snippets/pipeAsyncFunctions.md @@ -11,13 +11,14 @@ const pipeAsyncFunctions = (...fns) => arg => fns.reduce((p, f) => p.then(f), Pr ``` ```js + const sum = pipeAsyncFunctions( x => x + 1, x => new Promise(resolve => setTimeout(() => resolve(x + 2), 1000)), x => x + 3, async x => (await x) + 4 ); -(async () => { +(async() => { console.log(await sum(5)); // 15 (after one second) })(); ``` diff --git a/snippets/remove.md b/snippets/remove.md index a8c472774..1c457d2d9 100644 --- a/snippets/remove.md +++ b/snippets/remove.md @@ -6,12 +6,13 @@ Use `Array.prototype.filter()` to find array elements that return truthy values The `func` is invoked with three arguments (`value, index, array`). ```js + const remove = (arr, func) => Array.isArray(arr) ? arr.filter(func).reduce((acc, val) => { - arr.splice(arr.indexOf(val), 1); - return acc.concat(val); - }, []) + arr.splice(arr.indexOf(val), 1); + return acc.concat(val); + }, []) : []; ``` diff --git a/test/_30s.js b/test/_30s.js index 9cc89cd06..864116948 100644 --- a/test/_30s.js +++ b/test/_30s.js @@ -241,13 +241,14 @@ const differenceBy = (a, b, fn) => { return a.filter(x => !s.has(fn(x))); }; const differenceWith = (arr, val, comp) => arr.filter(a => val.findIndex(b => comp(a, b)) === -1); + const dig = (obj, target) => target in obj ? obj[target] : Object.values(obj).reduce((acc, val) => { - if (acc !== undefined) return acc; - if (typeof val === 'object') return dig(val, target); - }, undefined); + if (acc !== undefined) return acc; + if (typeof val === 'object') return dig(val, target); + }, undefined); const digitize = n => [...`${n}`].map(i => parseInt(i)); const distance = (x0, y0, x1, y1) => Math.hypot(x1 - x0, y1 - y0); const drop = (arr, n = 1) => arr.slice(n); @@ -316,11 +317,12 @@ const extendHex = shortHex => .split('') .map(x => x + x) .join(''); + const factorial = n => n < 0 ? (() => { - throw new TypeError('Negative numbers are not allowed!'); - })() + throw new TypeError('Negative numbers are not allowed!'); + })() : n <= 1 ? 1 : n * factorial(n - 1); @@ -960,12 +962,13 @@ const reducedFilter = (data, keys, fn) => }, {}) ); const reject = (pred, array) => array.filter((...args) => !pred(...args)); + const remove = (arr, func) => Array.isArray(arr) ? arr.filter(func).reduce((acc, val) => { - arr.splice(arr.indexOf(val), 1); - return acc.concat(val); - }, []) + arr.splice(arr.indexOf(val), 1); + return acc.concat(val); + }, []) : []; const removeNonASCII = str => str.replace(/[^\x20-\x7E]/g, ''); const renameKeys = (keysMap, obj) =>