Methods of an array Back
Basic Operations
1. concat(arrayX, arrayX, ..., arrayX)
concat(arrayX, arrayX, ..., arrayX) is used to put more than two arrays into one, and return.
const a = [1, 2, 3];
console.log(a.concat(4, 5)); /** => [1, 2, 3, 4, 5] */
const b = [4, 5];
const c = [6];
console.log(a.concat(b, c)); /** => [1, 2, 3, 4, 5, 6] */
concat(arrayX, arrayX, ..., arrayX) will return an new array copy, without changing the original one.
2. join(separator)
join(separator) is used to put items in an array into an string, with a separator.
const a = ['Hello', 'World'. 'Aleen'];
console.log(a.join(', ')); /** => Hello, World, Aleen */
3. pop() & shift()
pop() is used to delete and return the last item of an array.
shift() is used to delete and return the first item of an array.
const a = [1, 2, 3, 4, 5, 6];
console.log(a.pop()); /** => 6 */
console.log(a); /** => [1, 2, 3, 4, 5] */
console.log(a.shift()); /** => 1 */
console.log(a); /** => [2, 3, 4, 5] */
4. push(item1, item2, ..., itemX) & unshift(item1, item2, ..., itemX)
push(item1, item2, ..., itemX) is used to push one item into the last position of an array, and return the new length of this array.
unshift(item1, item2, ..., itemX) is used to push one item into the first position of an array, and return the new length of this array.
const a = [2, 3, 4, 5];
console.log(a.push(6)); /** => 5 */
console.log(a); /** => [2, 3, 4, 5, 6] */
console.log(a.unshift(1)); /** => 6 */
console.log(a); /** => [1, 2, 3, 4, 5, 6] */
5. reverse()
reverse() is used to reverse the order of an array.
const a = [1, 2, 3, 4, 5];
console.log(a.reverse()); /** => [5, 4, 3, 2, 1] */
console.log(a); /** => [5, 4, 3, 2, 1] */
reverse() will change the original array, rather than creating a new copy
6. sort(sortby)
sort(sortby) will have a sort of an array, based on the character or the number among them.
- sortby(optional): must be a function to specify which is the before one
- function sortby(a, b)
- return <0: a is the before one
- return =0: a or b can be the before one
- return >0: b is the before one
- function sortby(a, b)
const a = [3, 5, 1, 2, 4];
console.log(a.sort()); /** => [1, 2, 3, 4, 5] */
function sortby(a, b) {
return b - a;
}
console.log(a.sort(sortby)); /** => [5, 4, 3, 2, 1] */
sort(sortby) will change the original array, rather than creating a new copy
7. slice(start, end) & splice(index, howmany, item1, item2, ..., itemX)
slice(start, end) is used to get items of an array from the start to the end. (not include the end)
splice(index, howmany, item1, item2, ..., itemX) is used to add/remove items of an array from the index, and add before deleting howmany items.
- end(optional): specify when to end, which is equivalent to the (length + 1) of the array.
const a = [1, 2, 3, 4, 5];
console.log(a.slice(2, 4)); /** => [3, 4] */
console.log(a.slice(1)); /** => [2, 3, 4, 5] */
console.log(a.slice(3, 4)); /** => [4] */
slice(start, end) will return an new array copy, without changing the original one.
const a = [1, 2, 3, 4, 5];
console.log(a.splice(0, 2, 7, 8)); /** => [7, 8, 3, 4, 5] */
console.log(a.splice(4, 0, 1)); /** => [1, 2, 3, 4, 5, 1] */
splice(index, howmany, item1, item2, ..., itemX) will change the original array, rather than creating a new copy
8. toString() && toLocaleString()
Both toString() and toLocaleString() will return a string, but the method toLocalString() will return various result according to the local environment like time.
const a = [1, 2, 3, 4];
console.log(a.toString()); /** => 1,2,3,4 */
console.log(a.toLocaleString()); /** => 1,2,3,4 */
console.log(a.join()); /** => 1,2,3,4 */
console.log(a.join(,)); /** => 1,2,3,4 */
console.log(a.join() === a.toString()); /** => true */
Sets Operations
1. each()
/**
* [each: iterate each item of an array]
* @param {Function} fn [iterating function]
* @return {[type]} [description]
*/
Array.prototype.each = function (fn) {
/** fn is assigned to Function.K by default */
fn = fn || Function.K;
/** a set of results */
var a = [];
/** get arguments into an array except the first argument */
var args = Array.prototype.slice.call(arguments, 1);
/** loop to call function */
for (var i = 0; i < this.length; i++) {
/** apply arguments to the function to call */
var res = fn.apply(this, [this[i], i].concat(args));
if (res !== null) {
/** push the result into the array and return eventually */
a.push(res);
}
}
return a;
}
2. uniquelize()
/**
* [uniquelize: remove replicate items from an array]
* @return {[type]} [description]
*/
Array.prototype.uniquelize = function () {
var ra = new Array();
for (var i = 0; i < this.length; i++) {
if (!ra.contains(this[i])) {
ra.push(this[i]);
}
}
return ra;
}
3. intersect(a, b)
Array.intersect = function (a, b) {
return a.uniquelize().each(function (o) {
return b.includes(o) ? o : null;
});
};
4. union(a, b)
Array.union = function (a, b) {
return a.concat(b).uniquelize();
};
5. minus(a, b)
Array.minus = function (a, b) {
return a.uniquelize().each(function (o) {
return b.includes(o) ? null : o;
});
};
6. complement(a, b)
Array.complement = function (a, b) {
return Array.minus(Array.union(a, b), Array.intersect(a, b));
}
Feature Operations
1. Array.of(element0, element1, ..., elementX)
Array.of(element0, element1, ..., elementX) is used to put mutiple elements into one array and return a new array instance.
console.log(Array.of(1)); /** => [1] */
console.log(Array.of(undefined)); /** => [undefined] */
Polyfill:
if (!Array.of) {
Array.of = function() {
return Array.prototype.slice.call(arguments);
};
}
2. Array.from(obj, mapFn, thisArg)
Array.from(obj, mapFn, thisArg) is used to convert a array-like object into an array.
Those two kindes of array-like objects can be converted into arries:
- Array-like Object (with
lengthattribute, and any objects with keys) Iteratable Object (like Map, Set, and so on)
mapFn(optional): the map function which will be executed before the array return.
- thisArg(optional):
thisformapFn.
Array.from(obj, mapFn, thisArg);
Array.from(obj).map(mapFn, thisArg);
function convertIntoArray() {
return Array.from(argments);
}
console.log(convertIntoArray(1, 2, 3)); /** => [1, 2, 3] */
console.log(Array.from('foo')); /** => ["f", "o", "o"] */
Polyfill:
// Production steps of ECMA-262, Edition 6, 22.1.2.1
// Reference: https://people.mozilla.org/~jorendorff/es6-draft.html#sec-array.from
if (!Array.from) {
Array.from = (function () {
var toStr = Object.prototype.toString;
var isCallable = function (fn) {
return typeof fn === 'function' || toStr.call(fn) === '[object Function]';
};
var toInteger = function (value) {
var number = Number(value);
if (isNaN(number)) { return 0; }
if (number === 0 || !isFinite(number)) { return number; }
return (number > 0 ? 1 : -1) * Math.floor(Math.abs(number));
};
var maxSafeInteger = Math.pow(2, 53) - 1;
var toLength = function (value) {
var len = toInteger(value);
return Math.min(Math.max(len, 0), maxSafeInteger);
};
// The length property of the from method is 1.
return function from(arrayLike/*, mapFn, thisArg */) {
// 1. Let C be the this value.
var C = this;
// 2. Let items be ToObject(arrayLike).
var items = Object(arrayLike);
// 3. ReturnIfAbrupt(items).
if (arrayLike == null) {
throw new TypeError("Array.from requires an array-like object - not null or undefined");
}
// 4. If mapfn is undefined, then let mapping be false.
var mapFn = arguments.length > 1 ? arguments[1] : void undefined;
var T;
if (typeof mapFn !== 'undefined') {
// 5. else
// 5. a If IsCallable(mapfn) is false, throw a TypeError exception.
if (!isCallable(mapFn)) {
throw new TypeError('Array.from: when provided, the second argument must be a function');
}
// 5. b. If thisArg was supplied, let T be thisArg; else let T be undefined.
if (arguments.length > 2) {
T = arguments[2];
}
}
// 10. Let lenValue be Get(items, "length").
// 11. Let len be ToLength(lenValue).
var len = toLength(items.length);
// 13. If IsConstructor(C) is true, then
// 13. a. Let A be the result of calling the [[Construct]] internal method of C with an argument list containing the single item len.
// 14. a. Else, Let A be ArrayCreate(len).
var A = isCallable(C) ? Object(new C(len)) : new Array(len);
// 16. Let k be 0.
var k = 0;
// 17. Repeat, while k < len… (also steps a - h)
var kValue;
while (k < len) {
kValue = items[k];
if (mapFn) {
A[k] = typeof T === 'undefined' ? mapFn(kValue, k) : mapFn.call(T, kValue, k);
} else {
A[k] = kValue;
}
k += 1;
}
// 18. Let putStatus be Put(A, "length", len, true).
A.length = len;
// 20. Return A.
return A;
};
}());
}
3. Array.isArray(value)
Array.isArray(value) is used to justify whether the value is an array.
Polyfill:
if (!Array.isArray) {
Array.isArray = function (obj) {
return Object.prototype.toString.call(obj) === '[Object Array]';
}
}
4. filter(callback, thisArg)
filter(callback, thisArg) is used to filter all elements in an array, and create a new one for which get true from callback.
- thisArg(optional):
thisforcallback.
console.log([12, 5, 8, 130, 44].filter(function (item) {
return item >= 10;
})); /** => [12, 130, 44] */
console.log([12, 5, 8, 130, 44].filter(function (item, i) {
return item >= 10 && (i % 2 === 0);
})); /** => [12, 44] */
Polyfill:
if (!Array.prototype.filter) {
Array.prototype.filter = function (fun /*, thisArg */) {
"use strict";
if (this === void 0 || this === null) {
throw new TypeError();
}
var t = Object(this);
var len = t.length >>> 0;
if (typeof fun !== "function") {
throw new TypeError();
}
var res = [];
var thisArg = arguments.length >= 2 ? arguments[1] : void 0;
for (var i = 0; i < len; i++) {
if (i in t) {
var val = t[i];
// NOTE: Technically this should Object.defineProperty at
// the next index, as push can be affected by
// properties on Object.prototype and Array.prototype.
// But that method's new, and collisions should be
// rare, so use the more-compatible alternative.
if (fun.call(thisArg, val, i, t)) {
res.push(val);
}
}
}
return res;
};
}
5. some(callback, thisArg)
some(callback, thisArg) is used to test whether some element in the array passes the test implementation by the provided function.
- callback: a provided function which take three arguments:
- currentValue: the current element being passed
- index: the index of the current element being passed
- array: the array some() was called upon
- thisArg(optional):
thisformapFn.
function isBiggerThan10(element, index, array) {
return element > 10;
}
console.log([2, 5, 8, 1, 4].some(isBiggerThan10)); /** => false */
console.log([12, 5, 8, 1, 4].some(isBiggerThan10)); /** => true */
polyfill:
// Production steps of ECMA-262, Edition 5, 15.4.4.17
// Reference: http://es5.github.io/#x15.4.4.17
if (!Array.prototype.some) {
Array.prototype.some = function(fun/*, thisArg*/) {
'use strict';
if (this == null) {
throw new TypeError('Array.prototype.some called on null or undefined');
}
if (typeof fun !== 'function') {
throw new TypeError();
}
var t = Object(this);
var len = t.length >>> 0;
var thisArg = arguments.length >= 2 ? arguments[1] : void 0;
for (var i = 0; i < len; i++) {
if (i in t && fun.call(thisArg, t[i], i, t)) {
return true;
}
}
return false;
};
}