Using array methods in JavaScript to summarize _javascript tips

Defining arrays

Copy Code code as follows:

Var Arrymap = {riskid: "<%=riskid%>", Risktype: "<%=risktype%>"};

Or

Copy Code code as follows:

Var Arry =[];

Use:

var risk = Arrymap.riskid;
Arry.push ({id: "1", Name: "1"});
Arry.push ({ID: "2", Name: "2"});

A single value can also be placed in an array

Such as:

var data2 = [];
Data2.push (1);
Data2.push (2);

Loop Array Value

Var data1 =[2];
Data1 = Arry;
If (Data1!=null) {for
(var i at last) {
var lat = last[i];
Alert (lat.id);
Alert (Lat.name);
}
}

Output: 1 1 2 2

The use of arrays in JS

1, the creation of the array

var name= new Array (); Create an array
name[0]= "Zhangsan";//Assign value to array
name[1]= "Lisi";
var arrayobj = new Array ([size]); Create an array and specify the length, note that is not the upper limit, is the length
var name=["Zhangsan", "Lisi"];//Create an array and assign the
var name=new array ("Zhangsan", "Lisi") ;

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[1]; Gets the element value of the array
arrayobj[1]= "This is the new value";//give the array element a new value

3, the addition of array elements

Arrayobj. Push ([Item1 [item2 [...] [Itemn]]]); /Adds one or more new elements to the end of the array and returns an array of new length
arrayobj.unshift ([Item1 [item2]. [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,0,[item1[, item2[, ...). [, 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 (); Remove the last element and return the element value
arrayobj.shift ();//Remove the first element and return 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 will replicate all elements arrayobj.concat after start
([item1[, item2[, ...). [, 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 (0); 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 elements (top to last, last row to top), return array address
arrayobj.sort ();//////array element sort

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=[12,23,5,3,25,98,76,54,56,76];
Defines an array alert (Arr.length) that contains 10 digits,
///Displays the length of the array
arr.length=12;//increases the length of the array
alert (arr.length); Displays the length of the array changed to
alert (arr[8]);//Displays the value of the 9th element,
arr.length=5;//Reduce the length of the array to 5, and the elements indexed equal to or more than 5 are discarded
alert (arr[8]) ; shows that the 9th element has changed to "undefined"
arr.length=10;//Restores the array length to ten
alert (arr[8]);//Although the length is restored to 10, the 9th element cannot be retracted, displaying the 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];
alert (arr.length);
arr[15]=34;
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[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

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

For arrays:

y = new Array ();