Md Toy Blog

Javascript functions



Array : Pure

  • concat([value1[, value2[, ...[, valueN]]]]): merges many arrays together : a1.concat([1, 2], a3, a4), returns the merged array.
  • Array.from(): creates a new, shallow copied Array instance from an array like or iterable object Array.from("hey", x => x.toUpperCase()); //["H", "E", "Y"]
  • filter(callback(element[, index[, array]])[, thisArg]): creates a new array with all the elements that pass the test in callback.
  • map(callback( currentValue[, index[, array]])): returns new array populated with the results of calling callback on every element of the calling array.
  • reduce(callback( accumulator, currentValue[, index[, array]] )[, initialValue]): executes callback on each element of the array, resulting in a single output value.
  • reduceRight(callback(accumulator, currentValue[, index[, array]])[, initialValue]): same as reduce but starts reducing from the end
  • slice([begin[, end]]): returns a shallow copy of a portion of an array into a new array object, selected from begin to end both being indexes.
  • join([spearator]): joins and creates a new string from the elements of calling array-like.
  • flat([depth]): creates a new array with all sub-array elements extracted and put in the first level array
  • flatMap(callback(currentValue[, index[, array]])[, thisArg]) map but calls flat on the resulting array.
  • includes(valueToFind[, fromIndex]) returns true if valueToFind is found in array, false otherwise. Can find an object reference.
  • lastIndexOf(searchElement[, fromIndex]) same as includes except it returns the index if found or -1 otherwise.
  • indexOf(searchElement[, fromIndex]) same as lastIndexOf except it starts searching from the end.
  • keys(): returns a new array with the keys
  • values(): returns a new array iterator containing the values for each index in the array
  • some(callback[, thisArg]): returns true if there exists some element in the calling array for which callback returned true.
  • Object.assign
  • toString(): returns string version of the array.

Array : Impure

  • push(element1[, ...[, elementN]): add element to end of array. ret = a.push(el): ret is count of elements in a after push. a contains. Similar pure version concat
  • pop(): removes the last element from the calling array and returns that element.
  • forEach(callback(currentValue [, index [, array]])[, thisArg]) : perform callback on each element of array. Returns undefined. No way to stop or break a forEach() use for...of / or every(), some(), find() or findIndex().
  • pop() removes the last element from the calling array, and returns that element.
  • shift(): removes the first element from the calling array and returns that element.
  • unshift(element1[, ...[, elementN]]]): add elements to the front of array. Returns modified array length.
  • reverse(): reverses the calling array in place.
  • sort([compareFunction(firstEl, secondEl)]): sorts the elements of the calling array, ascending by default, built upon converting the elements into strings, then comparing their sequences of UTF-16 code unit values. The compareFunction should return -1 if firstEl has less priority than seondEl, 1 for the contrary, and 0 in case of equal priority.
  • splice(start[, deleteCount[, item1[, item2[, ...]]]]): optionally insert item1, item2... into the calling array, by optionally removing deleteCount elements starting at index start. If only start is provided, returns the first start elements.



  • arguments
  • length
  • name


  • apply(thisArg[, argsArray]) calls a function with a given this value and arguments provided as an array, like in apply
  • bind(thisArg[, arg1[, arg2[, ...argN]]]) method creates a new function that when called has its this keyword set to thisArg, and is passed the arg1, … prepended to the actual call arguments
  • call(thisArg[, arg1[, arg2[, ...argN]]]) same as apply but arguments are provided as arguments to call
  • toString()