Getting Started those things array of JavaScript

The concept of an array: the referenced object type.

1. Essence: a plurality of data stored in memory space, and then a name.
2. Data structures: different data structures, different good operation.
3. An array of features: easy to find and maintain data.

Creating an array:

1. Method 1: var array element name = [1, element 2, element 3 ...... n] element;
2. Note: You can create an empty array, it is recommended to create an assignment at the same time!
3. Mode 2: var array name = new Array ();

An array of Use:

1. Index: Each element has a room number for the default starting from 0, incremented by one.
2. Element: in fact, saved in a data array, can be a variety of data types.
3. Have access to an array of elements: the use of elements in the array and ordinary variables exactly the same.
4. Use array name [subscript]: Gets the underlying data in the correspondence.
5. Using the array name [index] = new value: the new value replaces the original value.

An array of attributes:

1. .length attribute: record the number of array elements theoretically. The actual saving is the last element at +1 standard array. The number and the actual length of the element is not necessarily the same.
2. Note: length from the array can not be used alone, do not need to manually modify automatically maintained.

Common operations:

1. Get the last element in the array: arr [arr.length-1];
2. Get the penultimate element of the n-th elements: arr [arr.length-n];
3. At the end of the array pursue a new element:. Arr [] = arr.length new element;
4. Modify the array's length property, you can achieve the purpose of deleting elements!
5. Removes the last element in the array: arr.length--;
6. Delete the last n elements of the array: arr.length- = n;
7. About the nature of the array: type of reference object
8. Output: dir: structure and contents of the output data, rather than immediately output, click on the small triangle after the output of the right content in memory!
9. Traversal: each element of the array in order to find, and do the same!

　　　　　　for (var i=0;i<=arr.length;i++) {
　　　　　　　　arr[i];
　　　　　　}　　

Array Category:

1. Indexed array: array subscript numbers
2. Associative array: Custom index value
3. Create an array: var arr = []; // create an empty array; arr [ "subscript name"]; = value; add a new element to an empty array, and a custom index names.
4. Using arrays: general arrays as elements, use the same general array. Value: arr [index name] assignment: arr [index] = Name the new value;
5. Note: length attribute associative array failure, always 0;
6. Traversal: for in looping through an associative array!　　

　　　　　　for(var key in arr) {
　　　　　　　　arr[key];
　　　　　　}　　

Notes: key: for each cycle to save the underlying variables under temporary variables; in: Keywords; arr: array name needs to traverse an array

　　 7. Summary: an array of features: easy to maintain and search data!

　　 8. associative array vs indexed array: associative array: Find a faster and more efficient. The reason: direct positioning element, the search speed is not the number of elements influence; indexed array: relatively slow! The reason: Only traversal search, search efficiency by the number of elements, the position of influence!

API array

1. API: others have written, the program we used directly.
2. Array: storing a plurality of data, and the operation of these API objects to provide data.
3. String into an array

3.1 string（arr）;　　arr.toString();

3.2 API can be more than two indexed array to a string. ------ each element in the array and then converted to string between "," stitching.

3.3 arr.join ( "splice symbol"); each element in the array of the specified character spliced ​​splicing. Note: If the stitching is omitted, default use "," mosaic.

3.4 fixed routine:

var str="<ANY>"+arr.join("</ANY><ANY>")+"</ANY>"
　　　　　　　　　　　 elem.innerHTML=str；

4. Select the array splice

　 4.1 splicing: splice multiple elements or array to a new array;

 var new_arr=old_arr.concat（值，数组）；

　 Note: concat (); return new array, without modifying the original array; if required stitching is an array, the array elements to break one element in the mosaic!

　 4.2 Select: selection element between the positions specified in the array, a new array returned composition.

  var new_arr=old_arr.slice(starti,endi);

　　Note: Do not modify the original array

　 If an API parameters are two subscripts, typically containing free end of the head!

slice（starti，starti+n）；//n表示选取元素的个数

　　 Support negative argument: the principle of using the length property.

arr.slice(starti,-n)<=>arr.slice(starti,arr.length-n);

Not all API supports negative parameters, use arr.length-n.

The second parameter is omitted: Select from the starting position up to the end.

var new_arr=arr.slice();

　　While omitting two parameters: copy the array;

var new_arr=arr.slice();

CRUD ---- splice 5. array

Increased 5.1: arr.splice (starti, 0, the value 1, value 2, value ...... value n-3);

　　Note: The new value is inserted after the specified position, all subsequent shift positions that order; if the value of the array is inserted, not broken, the specified position is inserted between the array.

　 5.2 Delete:

arr.splice(starti,n);　　//从starti位置开始删除n个元素

　 Note: directly modify the original array; support a negative argument; you can omit the second argument ---- has been deleted to the end; there is new data ---- return the deleted elements of value.

　5.3 Review:

arr.splice(starti,n,值1，值2.....);　　其实就是将原值删除，加入新值！　　//从starti位置开始，删除n个元素，在加入新值

　 Note: Deleting elements need not be consistent with the preservation number of elements inserted!

6. Sort:

　6.1 Flip ---- Reverse:

　　arr.reverse();　　//将元素组中的元素按原顺序颠倒！

　　　 Note: directly modify the original array, not return the new value; can not modify the content of the order, but the head and tail upside down!

　　　Sequential ordering 6.2: arr.sort (comparator function); // according to the contents of the array to a small large / small to large by sequential ordering!

　　 Note: The default parameter is not passed, the data in the array in ascending order; directly modifying the original array, not return the new value!

　　　 Principle: sort by default elements in the array into a string, and then follow the character encoding compare the size!

　　　6.3 comparator functions: one by one comparison between the size of two elements.

format:

function comp（a,b）{
　　　　　　return a-b;
　　　　　　　       }

　　　　 If a> b, need to return a number greater than 0!

　　　　 If a = b, the need to return a number equal to 0!

　　　　 If a <b, a need to return the number of less than 0!

7. Stack: open end, a closed end array structure!

7.1 stack, the stack:

　 Stack: remove an element from the array.

　 Stack: add an element to the array.

　 Data structure with both ends open: 7.2 queue

8. The two-digit groups:

8.1

      eg：var arr=[[1,2,3,4],[3,4,5,6],[6,7,8,9]];

　　 8.2 traversing two-dimensional array: two steps: 1, to obtain a two-dimensional array of each sub-array; 2, traversing each subarray!

 

JavaScript some of the information

- JS knowledge Summary -

http://www.makeru.com.cn/live/1396_592.html?s=45051

- Into the JavaScript function in the world -

http://www.makeru.com.cn/live/1396_1016.html?s=45051