ECMAScript 3 defines some useful functions that operate on arrays in it, which means that these functions are available as methods of any array.
1. () method
The () method converts all elements in the array into strings and concatenates them together, returning the last generated string. You can specify an optional symbol or string to separate the elements of the array in the generated string. If no delimiter is specified, a comma is used by default. Note: This method does not change the original array
var arr = ['a', 'b', 'c'];
(()); // a,b,c
((" ")); // a b c
(("")); // abc
(("slf")); // aslfbslfc
var arr2 = new Array(10);
(("-")); // ---------
Extension: The () method is an inverse operation of the () method, which divides the string into several blocks to create an array.
2. () method
The () method reverses the elements in the array in the reverse order and returns the array in reverse order. It takes the replacement; in other words, it does not create new arrays through rearranged elements, but rearranges them in the original array. Note: This method changes the original array.
var arr = ['a', 'b', 'c']; (()); // ['c', 'b', 'a'] (arr); // ['c', 'b', 'a']
3. () method
The () method sorts the elements in the array and returns the sorted array. When the sort() method is called without parameters, the array elements are sorted in alphabetical order. Note: This method changes the original array.
var arr = ['ba', 'b', 'ac']; (()); // ['ac', 'b', 'ba'] (arr); // ['ac', 'b', 'ba']
If the array contains undefined elements, they are placed at the end of the array.
var arr = new Array(4); arr[0] = 'ba'; arr[1] = 'b'; arr[2] = 'zc'; arr[3] = undefined; (()); // ['ac', 'b', 'ba', undefined] (arr); // ['ac', 'b', 'ba', undefined]
If you want to sort the array in other ways rather than alphabetical order, you must pass a comparison function to the sort() method. This function determines the order of its two parameters in a sorted array. Assuming the first parameter is in front of the comparison function should return a value less than 0. Conversely, assuming the first parameter is after, the function should return a value greater than 0. And, assuming that the two values are equal (their order does not matter), the function should return 0. For example, array sorting is done by numerical size rather than alphabetical order, the code is as follows:
var arr = new Array(4);
arr[0] = 45;
arr[1] = 12;
arr[2] = 103;
arr[3] = 24;
(()); // [103, 12, 24 45]
((function(a, b){return b-a;})); // [103, 45, 24, 12]
Sometimes you need to perform case-insensitive alphabet sorting on an array of strings. You can use the comparison function, first convert all parameters into lowercase strings (using the toLowerCase() method), and then start comparing.
var arr = ['abc', 'Def', 'BoC', 'FED'];
(()); // ["BoC", "Def", "FED", "abc"]
((function(s, t){
var a = ();
var b = ();
if (a < b) return -1;
if (a > b) return 1;
return 0;
})); // ["abc", "BoC", "Def", "FED"]
4. () Method
The () method creates and returns a new array whose elements include the elements of the original array that calls concat() and each parameter of concat(). If any of these parameters are themselves an array, then the elements of the array are connected, not the array itself. But be aware that concat() does not flatten the array of arrays recursively. Note: This method
The original array will not be modified.
var arr = ['abc', 'Def', 'BoC', 'FED']; ((1, 2)); // ["abc", "Def", "BoC", "FED", 1, 2] ((1, 2, [4, 5])); // ["abc", "Def", "BoC", "FED", 1, 2, 4, 5] ((1, 2, [4, ['slf', 5]])); // ["abc", "Def", "BoC", "FED", 1, 2, 4, Array[2]] (arr); // ["abc", "Def", "BoC", "FED"]
5. () method
The () method returns a fragment or subarray of the specified array. Its two parameters specify the beginning and end positions of the fragment respectively. The returned array contains all array elements between the position specified by the first parameter and all the positions specified by the second parameter (but not the position specified by the second parameter). If only one parameter is specified, the returned array will contain all elements from the start position to the end of the array. If a negative number appears in the parameter, it indicates the position relative to the last element in the array. For example, parameter -1 specifies the last element, while -3 specifies the third last element. Note that this method does not modify the original array.
var arr = ['abc', 'Def', 'BoC', 'FED', 'slf']; ((1, 2)); // ["Def"] ((3)); // ["FED", 'slf'] ((0, -1)); // ['abc', 'Def', 'BoC', 'FED'] ((-3, -1)); // ['BoC', 'FED'] (arr); // ['abc', 'Def', 'BoC', 'FED', 'slf']
6. () Method
The () method is a common method to insert or delete elements in an array. Note that splice() and slice() have very similar names, but their functions are essentially different. splice() can delete elements from an array, insert elements into an array, or complete both operations at the same time. Array elements after inserting or deleting points will increase or decrease their index values as needed, so the rest of the array remains continuous. The first parameter of splice() specifies the start position for insertion and/or deletion. The second parameter specifies the number of elements that should be deleted from the array. If the second parameter is omitted, all elements from the start point to the end of the array will be deleted. splice() returns an array composed of deleted elements, or an empty array if no deleted elements are returned. Note: This method changes the original array. (Different from concat(), splice() inserts the array itself rather than the elements of the array.)
var arr = [1, 2, 3, 4, 5, 6, 7, 8, 9]; ((7)); // [8, 9] (arr); // [1, 2, 3, 4, 5, 6, 7] ((2, 4)); // [3, 4, 5] (arr); // [1, 2, 7] ((2, 1, 3, 4, 5, 6)); // [7] (arr); // [1, 2, 3, 4, 5, 6] ((3, 2, 3, [1, 2, 3])); // [4, 5] (arr); // [1, 2, 3, [1, 2, 3], 6]
7. () and () methods
The push() and pop() methods allow arrays to be used as stacks. The push() method adds one or more elements at the end of the array and returns the new length of the array. The pop() method is the opposite: it deletes the last element of the array, reduces the length of the array and returns the value it deletes. Note: Both methods modify the original array.
var arr = [1, 2, 3]; ((7)); // 4 (arr); // [1, 2, 3, 7] (([2, 4])); // 5 (arr); // [1, 2, 3, 7, [2, 4]] (()); // [2, 4] (arr); // [1, 2, 3, 7]
8. () and () methods
The behavior of unshift() and shift() methods is very similar to the push() and pop() methods. The difference is: the former is to insert and delete elements at the head of the array. unshift() adds one or more elements at the head of the array, moves existing elements to a higher index to get enough space, and finally returns the new length of the array. shift() deletes the first element of the array and returns the deleted element, then moves all subsequent elements forward by one position to fill the gap in the array header. Note: Both methods modify the original array.
var arr = [6, 2, 3, 4, 5, 6];
(()); // 6
(arr); // [2, 3, 4, 5, 6]
((['a', 'b'])); // 6
(arr); // [['a', 'b'], 2, 3, 4, 5, 6]
(('a', 'b')); // 8
(arr); // ['a', 'b', ['a', 'b'] 2, 3, 4, 5, 6]
Note that when unshift() is called with multiple parameters, if the parameters are inserted at one time rather than one at a time, this means that the order of the elements inserted in the final array is consistent with their order in the parameter list. And if elements are inserted one at a time, their order should be reversed.
var arr = [6, 2, 3, 4, 5, 6];
(('a', 'b', 'c')); // 9
(arr); // ['a', 'b', 'c', 6, 2, 3, 4, 5, 6]
((1)); // 10
(arr); // [1, 'a', 'b', 'c', 6, 2, 3, 4, 5, 6]
((2)); // 11
(arr); // [2, 1, 'a', 'b', 'c', 6, 2, 3, 4, 5, 6]
9. () and () methods
Arrays have the toString() method like other JavaScript objects. For arrays, this method converts each element of the array into a string and outputs a comma-separated list of strings. Note: This method does not modify the original array (this is the same as the string returned by calling the join() method without any arguments)
var arr = [1, 2, 3]; (()); // 1,2,3 (typeof(())) // string (arr); // [1, 2, 3]
Extension: toLocaleString() is a localized version of the toString() method. It calls the element's toLocaleString() method to convert each array element into a string, and uses a localized separator to concatenate these strings to generate the final string.
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