Counts the occurences of a value in an array.
+Counts the occurrences of a value in an array.
Use Array.reduce() to increment a counter each time you encounter the specific value inside the array.
const countOccurrences = (arr, value) => arr.reduce((a, v) => v === value ? a + 1 : a + 0, 0);
// countOccurrences([1,1,2,1,2,3], 1) -> 3
@@ -271,7 +272,7 @@ Use Array.reduce() to create an object, where the keys are produced
// initial([1,2,3]) -> [1,2]
Initialized an array containing the numbers in the specified range.
+Initializes an array containing the numbers in the specified range.
Use Array(end-start) to create an array of the desired length, Array.map() to fill with the desired values in a range.
You can omit start to use a default value of 0.
const initializeArrayWithRange = (end, start = 0) =>
@@ -297,6 +298,16 @@ You can omit value to use a default value of 0.
const last = arr => arr[arr.length - 1];
// last([1,2,3]) -> 3
+Maps the values of an array to an object using a function, where the key-value pairs consist of the original value as the key and the mapped value.
+Use an anonymous inner function scope to declare an undefined memory space, using closures to store a return value. Use a new Array to stor the array with a map of the function over its data set and a comma operator to return a second step, without needing to move from one context to another (due to closures and order of operations).
const mapObject = (arr, fn) =>
+ (a => (a = [arr, arr.map(fn)], a[0].reduce( (acc,val,ind) => (acc[val] = a[1][ind], acc), {}) )) ( );
+/*
+const squareIt = arr => mapObject(arr, a => a*a)
+squareIt([1,2,3]) // { 1: 1, 2: 4, 3: 9 }
+*/
+Returns the nth element of an array.
Use Array.slice() to get an array containing the nth element at the first place.
@@ -372,7 +383,7 @@ This method also works with strings.
Returns an array with n elements removed from the beggining.
+Returns an array with n elements removed from the beginning.
Use Array.slice() to create a slice of the array with n elements taken from the beginning.
const take = (arr, n = 1) => arr.slice(0, n);
// take([1, 2, 3], 5) -> [1, 2, 3]
@@ -419,7 +430,7 @@ If lengths of the argument-arrays vary, undefined is used where no
document.documentElement.clientHeight + window.scrollY >= document.documentElement.scrollHeight || document.documentElement.clientHeight;
// bottomVisible() -> true
Returns the current URL.
Use window.location.href to get current URL.
const currentURL = () => window.location.href;
@@ -780,7 +791,7 @@ const JSONToFile = (obj, filename) => fs.writeFile(`${filename}.json`, JSON.s
Returns an array of lines from the specified file.
Use readFileSync function in fs node package to create a Buffer from a file.
convert buffer to string using toString(encoding) function.
-creating an array from contents of file by spliting file content line by line(each \n).
+creating an array from contents of file by spliting file content line by line (each \n).
const fs = require('fs');
const readFileLines = filename => fs.readFileSync(filename).toString('UTF8').split('\n');
/*
@@ -797,7 +808,7 @@ console.log(arr) // -> ['line1', 'line2', 'line3']
cleanObj
Removes any properties except the ones specified from a JSON object.
Use Object.keys() method to loop over given json object and deleting keys that are not included in given array.
-also if you give it a special key(childIndicator) it will search deeply inside it to apply function to inner objects too.
+Also if you give it a special key (childIndicator) it will search deeply inside it to apply function to inner objects too.
const cleanObj = (obj, keysToKeep = [], childIndicator) => {
Object.keys(obj).forEach(key => {
if (key === childIndicator) {
@@ -852,7 +863,7 @@ Base cases are for string length equal to 2 or 1
Capitalize
Capitalizes the first letter of a string.
Use destructuring and toUpperCase() to capitalize first letter, ...rest to get array of characters after first letter and then Array.join('') to make it a string again.
-Omit the lowerRest parameter to keep the rest of the string intact, or set it to true to convert to lower case.
+Omit the lowerRest parameter to keep the rest of the string intact, or set it to true to convert to lowercase.
const capitalize = ([first,...rest], lowerRest = false) =>
first.toUpperCase() + (lowerRest ? rest.join('').toLowerCase() : rest.join(''));
// capitalize('myName') -> 'MyName'
@@ -873,7 +884,7 @@ Omit the lowerRest parameter to keep the rest of the string intact,
fromCamelCase
Converts a string from camelcase.
Use replace() to remove underscores, hyphens and spaces and convert words to camelcase.
-Omit the scond argument to use a default separator of _.
+Omit the second argument to use a default separator of _.
const fromCamelCase = (str, separator = '_') =>
str.replace(/([a-z\d])([A-Z])/g, '$1' + separator + '$2')
.replace(/([A-Z]+)([A-Z][a-z\d]+)/g, '$1' + separator + '$2').toLowerCase();
@@ -925,7 +936,7 @@ Return the string truncated to the desired length, with ... appende
getType
Returns the native type of a value.
-Returns lower-cased constructor name of value, "undefined" or "null" if value is undefined or null
+Returns lowercased constructor name of value, "undefined" or "null" if value is undefined or null
const getType = v =>
v === undefined ? 'undefined' : v === null ? 'null' : v.constructor.name.toLowerCase();
// getType(new Set([1,2,3])) -> "set"
diff --git a/tag_database b/tag_database
index 3d17b3376..562b3b388 100644
--- a/tag_database
+++ b/tag_database
@@ -13,7 +13,7 @@ collatz:math
compact:array
compose:function
countOccurrences:array
-current-URL:browser
+currentURL:browser
curry:function
deepFlatten:array
difference:array
@@ -57,6 +57,7 @@ JSONToDate:date
JSONToFile:node
last:array
lcm:math
+mapObject:array
median:math
nthElement:array
objectFromPairs:object