The method of JS operation array Array and the _javascript technique of attribute example

This article summarizes 3 properties of array arrays, length properties, prototype properties, constructor properties, and notes the 8 categories of array objects and the use of multiple methods, as follows:

3 Properties of an object
1, Length Property

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, 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=[12,23,5,3,25,98,76,54,56,76];//defines an array that contains 10 digits
alert (arr.length); Displays the length of the array 10
arr.length=12; Increase the length of an array
alert (arr.length); The length of the display array has changed to 12
Alert (arr[8]); Displays the value of the 9th element, which is 56
arr.length=5; Reduces the length of the array to 5, and the elements indexed equal to or more than 5 are discarded
Alert (arr[8]); Show 9th element has changed to "undefined"
arr.length=10; Restores the array length to 10
Alert (arr[8]); Although the length is restored to 10, the 9th element cannot be retracted, displaying "undefined"

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=[12,23,5,3,25,98,76,54,56,76];//defines an array that contains 10 digits
alert (arr.length);//Show 10
arr[15]=34;
alert (arr.length);//Show 16

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

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[0];
for (i = 1; 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

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
function MyFunc {
function body.
}

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

For arrays:
y = new Array ();

8 categories of array objects and multiple methods

1. The creation of the array

var arrayobj = new Array (); Create a default array with a length of 0
var arrayobj = new Array (size); Create an array of size lengths, notice that the length of the array is variable, so it is not the upper bound, it is the length
var arrayobj = new Array (item1,item2,); Create an array and assign an initial 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 arrayitemvalue=arrayobj[1]; Gets the element value of an array
Arrayobj[1]= "To give new value"; Give a new value to an array element

This article summarizes 3 properties of array arrays, length properties, prototype properties, constructor properties, and notes the 8 categories of array objects and the use of multiple methods, as follows:

3 Properties of an object
1, Length Property

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=[12,23,5,3,25,98,76,54,56,76];//defines an array that contains 10 digits
alert (arr.length); Displays the length of the array 10
arr.length=12; Increase the length of an array
alert (arr.length); The length of the display array has changed to 12
Alert (arr[8]); Displays the value of the 9th element, which is 56
arr.length=5; Reduces the length of the array to 5, and the elements indexed equal to or more than 5 are discarded
Alert (arr[8]); Show 9th element has changed to "undefined"
arr.length=10; Restores the array length to 10
Alert (arr[8]); Although the length is restored to 10, the 9th element cannot be retracted, displaying "undefined"

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=[12,23,5,3,25,98,76,54,56,76];//defines an array that contains 10 digits
alert (arr.length);//Show 10
arr[15]=34;
alert (arr.length);//Show 16

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

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[0];
for (i = 1; 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

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
function MyFunc {
function body.
}

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

For arrays:
y = new Array ();

8 categories of array objects and multiple methods

1. The creation of the array
var arrayobj = new Array (); Create a default array with a length of 0
var arrayobj = new Array (size); Create an array of size lengths, notice that the length of the array is variable, so it is not the upper bound, it is the length
var arrayobj = new Array (item1,item2,); Create an array and assign an initial 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 arrayitemvalue=arrayobj[1]; Gets the element value of an array
Arrayobj[1]= "To give new value"; Give a new value to an array element