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](https://github.com/iamsoorena)Logs the name of a function.
Use console.debug() and the name property of the passed method to log the method's name to the debug channel of the console.
const functionName = fn => (console.debug(fn.name), fn);
functionName(Math.max); // max (logged in debug channel of console)
-Returns the memoized (cached) function.
Use Object.create(null) to create an empty object without Object.prototype (so that those properties are not resolved if the input value is something like 'hasOwnProperty'). Return a function which takes a single argument to be supplied to the memoized function by first checking if the function's output for that specific input value is already cached, or store and return it if not.
const memoize = fn => {
- const cache = Object.create(null);
- return value => cache[value] || (cache[value] = fn(value));
+Returns the memoized (cached) function.
Create an empty cache by instantiating a new Map object. Return a function which takes a single argument to be supplied to the memoized function by first checking if the function's output for that specific input value is already cached, or store and return it if not. The function keyword must be used in order to allow the memoized function to have its this context changed if necessary. Allow access to the cache by setting it as a property on the returned function.
const memoize = fn => {
+ const cache = new Map();
+ const cached = function(val) {
+ return cache.has(val) ? cache.get(val) : cache.set(val, fn.call(this, val)) && cache.get(val);
+ };
+ cached.cache = cache;
+ return cached;
};
// See the `anagrams` snippet.
const anagramsCached = memoize(anagrams);
anagramsCached('javascript'); // takes a long time
anagramsCached('javascript'); // returns virtually instantly since it's now cached
+console.log(anagramsCached.cache); // Map
Ensures a function is called only once.
Utilizing a closure, use a flag, called, and set it to true once the function is called for the first time, preventing it from being called again. In order to allow the function to have its this context changed (such as in an event listener), the function keyword must be used, and the supplied function must have the context applied. Allow the function to be supplied with an arbitrary number of arguments using the rest/spread (...) operator.
const once = fn => {
let called = false;
return function(...args) {
@@ -717,10 +722,6 @@ isPrime(12); // false
};
lcm(12, 7); // 84
lcm([1, 3, 4], 5); // 60
-Returns the n maximum elements from the provided array. If n is greater than or equal to the provided array's length than return the original array(sorted in descending order).
Sort's the array's shallow copy in descending order and returns the first n elements
Skip the second argument to get a single element(in the form of a array)
const maxN = (arr, n = 1) => [...arr].sort((a, b) => b - a).slice(0, n);
-maxN([1, 2, 3]); // [3]
-maxN([1, 2, 3], 2); // [3,2]
-maxN([1, 2, 3], 4); // [3,2,1]
Returns the median of an array of numbers.
Find the middle of the array, use Array.sort() to sort the values. Return the number at the midpoint if length is odd, otherwise the average of the two middle numbers.
const median = arr => {
const mid = Math.floor(arr.length / 2),
nums = [...arr].sort((a, b) => a - b);
@@ -728,10 +729,6 @@ maxN([1, 2, 3], 4); // [3,2,1]
};
median([5, 6, 50, 1, -5]); // 5
median([0, 10, -2, 7]); // 3.5
-Returns the n minimum elements from the provided array. If n is greater than or equal to the provided array's length than return the original array(sorted in ascending order).
Sort's the array's shallow copy in ascending order and returns the first n elements
Skip the second argument to get a single element(in the form of a array)
const minN = (arr, n = 1) => [...arr].sort((a, b) => a - b).slice(0, n);
-minN([1, 2, 3]); // [1]
-minN([1, 2, 3], 2); // [1,2]
-minN([1, 2, 3], 4); // [1,2,3]
Uses the percentile formula to calculate how many numbers in the given array are less or equal to the given value.
Use Array.reduce() to calculate how many numbers are below the value and how many are the same value and apply the percentile formula.
const percentile = (arr, val) =>
100 * arr.reduce((acc, v) => acc + (v < val ? 1 : 0) + (v === val ? 0.5 : 0), 0) / arr.length;
percentile([1, 2, 3, 4, 5, 6, 7, 8, 9, 10], 6); // 55
diff --git a/snippets/memoize.md b/snippets/memoize.md
index 856375a69..fe753f8c8 100644
--- a/snippets/memoize.md
+++ b/snippets/memoize.md
@@ -10,9 +10,7 @@ Allow access to the `cache` by setting it as a property on the returned function
const memoize = fn => {
const cache = new Map();
const cached = function(val) {
- return cache.has(val)
- ? cache.get(val)
- : cache.set(val, fn.call(this, val)) && cache.get(val);
+ return cache.has(val) ? cache.get(val) : cache.set(val, fn.call(this, val)) && cache.get(val);
};
cached.cache = cache;
return cached;