Detailed JavaScript array operations Encyclopedia _javascript tips

This article introduces the operation of JS array is very detailed, interested friends to learn this article.

1, the creation of the array

var arrayobj = new Array (); Create an array
var arrayobj = new Array ([size]); Create an array and specify the length, note not the upper limit, is the length
var arrayobj = new Array ([element[, element[, ...)　[, ELEMENTN]]]); Create an array and assign a value

To illustrate, although the second method creates an array that specifies the length, in all cases the array is longer, that is, even if you specify a length of 5, you can still store the elements outside the specified length, note: the length changes.

2, access to elements of the array

var testgetarrvalue=arrayobj[]; Gets the element value of an array
Arrayobj[]= "This is the new value"; Give a new value to an array element

3, the addition of array elements

Arrayobj. push ([item [Item [...] [Itemn]]]); /Adds one or more new elements to the end of the array and returns the new length of the array
Arrayobj.unshift ([item] [item [...] [Itemn]]]); /Adds one or more new elements to the beginning of the array, the elements in the array are automatically moved back, and the new length of the array is returned
Arrayobj.splice (insertpos,,[item[, item[, ...) [, Itemn]]]); /inserts one or more new elements into the array at the specified position, and the element at the insertion point is automatically moved back to "".

4, the deletion of the elements of the array

Arrayobj.pop (); Removes the last element and returns the element value
Arrayobj.shift (); Removes the first element and returns the element value, and the elements in the array are automatically moved forward
Arrayobj.splice (Deletepos,deletecount); Deletes the specified number of DeleteCount elements starting at the specified position, deletepos the removed elements

5, the array of interception and merging

Arrayobj.slice (start, [end]); Returns a portion of an array as an array, noting that the end-corresponding element is not included, and if omitting the end copies all elements after start
Arrayobj.concat ([item[, item[, ...) [, Itemn]]]); Concatenate multiple arrays (or a string, or a mixture of arrays and strings) into an array, returning a new array of connections

6, the copy of the array

Arrayobj.slice (); Returns an array of copies, noting that a new array is not a pointer to the
Arrayobj.concat (); Returns an array of copies, noting that a new array is not a pointer to the

7, the ordering of array elements

Arrayobj.reverse (); Reverse element (top to last, last to top), return array address
Arrayobj.sort (); array element Sorting, returning the arrays address

8. String of array elements

Arrayobj.join (separator); Returns a string that connects each element value of an array, separated by a separator in the middle.
toLocaleString, toString, valueof: Can be seen as a special use of join, not commonly used

Two, 3 properties of an array object

1, Length Property

The Length property represents the size of the array, which is the number of elements. Because the index of an array always starts with 0, the upper and lower bounds of an array are: 0 and length-1 respectively. Unlike most other languages, the length property of a JavaScript array is variable, which requires special attention. When the length property is set larger, the state of the entire array does not actually change, only the length property is larger, and when the length property is set to the previous hour, the value of the element whose index is greater than or equal to length in the original array is lost. The following is an example of changing the length property:

var arr=[,,,,,,,,,];
Defines an array that contains a number
alert (arr.length); Display the length of an array
arr.length=; Increase the length of an array
alert (arr.length); The length of the display array has changed to
Alert (arr[]); Displays the value of the first element, which is
arr.length=; Reduces the length of an array to an element that is equal to or more than the index is discarded
Alert (arr[]); show that the first element has changed to "undefined"
arr.length=; Restores the array length to
Alert (arr[]); Although the length is restored, but the first element cannot be retracted, the "undefined" is displayed.

From the above code we can clearly see the nature of the length property. But the length object can be set not only explicitly, it may also be implicitly modified. You can use a variable that is not declared in JavaScript, and you can use an undefined array element (an element whose index exceeds or equal to length), at which point the value of the length property is set to the value plus 1 for the element index used. For example, the following code:

var arr=[,,,,,,,,,];
alert (arr.length);
arr[]=;
alert (arr.length);

The code also first defines an array of 10 digits, which can be seen by an alert statement of 10. Then the element with index 15 is assigned to 15, or arr[15]=34, and then the length of the array is output by the alert statement, with 16. In any case, this is a surprising feature for developers who are accustomed to strongly typed programming. In fact, an array created with the new Array () has an initial length of 0, and it is an operation that does not define an element in it, which changes the length of the array.

As you can see from the above introduction, the length property is so magical that it makes it easy to increase or decrease the size of the array. Therefore, a thorough understanding of the length attribute is helpful to the flexible application in the development process.

2, prototype property

Returns a reference to the object type prototype. The prototype property is common to object.

Objectname.prototype

The objectname parameter is the name of the object.

Description: Provides a set of basic functions for an object's class with the prototype property. The operation of the new instance of the object, "inherit", gives the object a prototype.

For an array object, use the following example to illustrate the purpose of the prototype property.

Adds a method to the array object that returns the maximum element value in the array. To do this, declare a function, add it to the Array.prototype, and use it.

function Array_max ()
 {
  var i,
  max = this[];
  for (i =; i < this.length; i++)
  {
    if (Max < this[i])
    max = this[i];
  return max;
}
Array.prototype.max = Array_max;
var x = new Array (1, 2, 3, 4, 5, 6);
var y = X.max ();

After the code executes, Y saves the maximum value in the array x, or says 6.

3, constructor property

Represents a function that creates an object.

Object.constructor//object is the name of an object or function.

Description: The constructor property is a member of all objects that have prototype. They include all of the JScript intrinsic objects except the Global and Math objects. The constructor property holds a reference to a function that constructs a particular object instance.

For example:

x = new String ("Hi");
if (X.constructor = = String)//To be processed (condition is true).
or
functions MyFunc {
  //function body.
}
y = new MyFunc;

if (Y.constructor = = MyFunc)//To be processed (condition is true)

For arrays:

y = new Array ();

The above is the entire narrative of this article, I hope you like.