JavaScript对象之数组Array的详细介绍
Array
Lets you work with arrays.
Core object |
|
Implemented in |
JavaScript 1.1, NES 2.0
JavaScript 1.3: added toSource method; changed length property; changed push method |
ECMA version |
ECMA-262 |
Created by
The Array object constructor:
new Array(arrayLength)
new Array(element0, element1, ..., elementN)
An array literal:
[element0, element1, ..., elementN]
JavaScript 1.2 when you specify LANGUAGE="JavaScript1.2" in the <SCRIPT> tag:
new Array(element0, element1, ..., elementN)
JavaScript 1.2 when you do not specify LANGUAGE="JavaScript1.2" in the <SCRIPT> tag:
new Array([arrayLength])
new Array([element0[, element1[, ..., elementN]]])
JavaScript 1.1:
new Array([arrayLength])
new Array([element0[, element1[, ..., elementN]]])
Parameters
arrayLength
|
The initial length of the array. You can access this value using the length property. If the value specified is not a number, an array of length 1 is created, with the first element having the specified value. The maximum length allowed for an array is 4,294,967,295. |
elementN
|
A list of values for the array's elements. When this form is specified, the array is initialized with the specified values as its elements, and the array's length property is set to the number of arguments. |
Description
An array is an ordered set of values associated with a single variable name.
The following example creates an Array object with an array literal; the coffees array contains three elements and a length of three:
coffees = ["French Roast", "Columbian", "Kona"]
You can construct a dense array of two or more elements starting with index 0 if you define initial values for all elements. A dense array is one in which each element has a value. The following code creates a dense array with three elements:
myArray = new Array("Hello", myVar, 3.14159)
Indexing an array. You index an array by its ordinal number. For example, assume you define the following array:
myArray = new Array("Wind","Rain","Fire")
You then refer to the first element of the array as myArray[0] and the second element of the array as myArray[1].
Specifying a single parameter. When you specify a single numeric parameter with the Array constructor, you specify the initial length of the array. The following code creates an array of five elements:
billingMethod = new Array(5)
The behavior of the Array constructor depends on whether the single parameter is a number.
-
If the value specified is a number, the constructor converts the number to an unsigned, 32-bit integer and generates an array with the length property (size of the array) set to the integer. The array initially contains no elements, even though it might have a non-zero length.
- If the value specified is not a number, an array of length 1 is created, with the first element having the specified value.
musicTypes = new Array(25)
musicTypes[0] = "R&B"
musicTypes[1] = "Blues"
musicTypes[2] = "Jazz"
Increasing the array length indirectly. An array's length increases if you assign a value to an element higher than the current length of the array. The following code creates an array of length 0, then assigns a value to element 99. This changes the length of the array to 100.
colors = new Array()
colors[99] = "midnightblue"
Creating an array using the result of a match. The result of a match between a regular expression and a string can create an array. This array has properties and elements that provide information about the match. An array is the return value of RegExp.exec, String.match, and String.replace. To help explain these properties and elements, look at the following example and then refer to the table below:
<SCRIPT LANGUAGE="JavaScript1.2">
//Match one d followed by one or more b's followed by one d
//Remember matched b's and the following d
//Ignore case
myRe=/d(b+)(d)/i;
myArray = myRe.exec("cdbBdbsbz");
</SCRIPT>
The properties and elements returned from this match are as follows:
Property/Element |
Description |
Example |
---|---|---|
input
|
A read-only property that reflects the original string against which the regular expression was matched. |
cdbBdbsbz |
index
|
A read-only property that is the zero-based index of the match in the string. |
1 |
[0]
|
A read-only element that specifies the last matched characters. |
dbBd |
[1], ...[n]
|
Read-only elements that specify the parenthesized substring matches, if included in the regular expression. The number of possible parenthesized substrings is unlimited. |
[1]=bB |
Backward Compatibility
JavaScript 1.2. When you specify a single parameter with the Array constructor, the behavior depends on whether you specify LANGUAGE="JavaScript1.2" in the <SCRIPT> tag:
-
If you specify LANGUAGE="JavaScript1.2" in the <SCRIPT> tag, a single-element array is returned. For example, new Array(5) creates a one-element array with the first element being 5. A constructor with a single parameter acts in the same way as a multiple parameter constructor. You cannot specify the length property of an Array using a constructor with one parameter.
- If you do not specify LANGUAGE="JavaScript1.2" in the <SCRIPT> tag, you specify the initial length of the array as with other JavaScript versions.
JavaScript 1.1 and earlier. When you specify a single parameter with the Array constructor, you specify the initial length of the array. The following code creates an array of five elements:
billingMethod = new Array(5)
JavaScript 1.0. You must index an array by its ordinal number; for example myArray[0].
Property Summary
Property |
Description |
---|---|
constructor
|
Specifies the function that creates an object's prototype. |
index
|
For an array created by a regular expression match, the zero-based index of the match in the string. |
input
|
For an array created by a regular expression match, reflects the original string against which the regular expression was matched. |
length
|
Reflects the number of elements in an array. |
prototype
|
Allows the addition of properties to all objects. |
Method Summary
Method |
Description |
---|---|
concat
|
Joins two arrays and returns a new array. |
join
|
Joins all elements of an array into a string. |
pop
|
Removes the last element from an array and returns that element. |
push
|
Adds one or more elements to the end of an array and returns the new length of the array. |
reverse
|
Transposes the elements of an array: the first array element becomes the last and the last becomes the first. |
shift
|
Removes the first element from an array and returns that element. |
slice
|
Extracts a section of an array and returns a new array. |
splice
|
Adds and/or removes elements from an array. |
sort
|
Sorts the elements of an array. |
toSource
|
Returns an array literal representing the specified array; you can use this value to create a new array. Overrides the Object.toSource method. |
toString
|
Returns a string representing the array and its elements. Overrides the Object.toString method. |
unshift
|
Adds one or more elements to the front of an array and returns the new length of the array. |
valueOf
|
Returns the primitive value of the array. Overrides the Object.valueOf method. |
In addition, this object inherits the watch and unwatch methods from Object.
Examples
Example 1. The following example creates an array, msgArray, with a length of 0, then assigns values to msgArray[0] and msgArray[99], changing the length of the array to 100.
msgArray = new Array()
msgArray[0] = "Hello"
msgArray[99] = "world"
// The following statement is true,
// because defined msgArray[99] element.
if (msgArray.length == 100)
myVar="The length is 100."
Example 2: Two-dimensional array. The following code creates a two-dimensional array and assigns the results to myVar.
myVar="Multidimensional array test; "
a = new Array(4)
for (i=0; i < 4; i++) {
a[i] = new Array(4)
for (j=0; j < 4; j++) {
a[i][j] = "["+i+","+j+"]"
}
}
for (i=0; i < 4; i++) {
str = "Row "+i+":"
for (j=0; j < 4; j++) {
str += a[i][j]
}
myVar += str +"; "
}
This example assigns the following string to myVar (line breaks are used here for readability):
Multidimensional array test;
Row 0:[0,0][0,1][0,2][0,3];
Row 1:[1,0][1,1][1,2][1,3];
Row 2:[2,0][2,1][2,2][2,3];
Row 3:[3,0][3,1][3,2][3,3];
concat
Joins two arrays and returns a new array.
Method of |
Array |
Implemented in |
JavaScript 1.2, NES 3.0 |
ECMA version |
ECMA-262 |
Syntax
concat(arrayName2, arrayName3, ..., arrayNameN)
Parameters
arrayName2... arrayNameN
|
Arrays to concatenate to this array. |
Description
concat does not alter the original arrays, but returns a "one level deep" copy that contains copies of the same elements combined from the original arrays. Elements of the original arrays are copied into the new array as follows:
-
Object references (and not the actual object): concat copies object references into the new array. Both the original and new array refer to the same object. If a referenced object changes, the changes are visible to both the new and original arrays.
- Strings and numbers (not String and Number objects): concat copies strings and numbers into the new array. Changes to the string or number in one array does not affect the other arrays.
The following code concatenates two arrays:
alpha=new Array("a","b","c")
numeric=new Array(1,2,3)
alphaNumeric=alpha.concat(numeric) // creates array ["a","b","c",1,2,3]
The following code concatenates three arrays:
num1=[1,2,3]
num2=[4,5,6]
num3=[7,8,9]
nums=num1.concat(num2,num3) // creates array [1,2,3,4,5,6,7,8,9]
constructor
Specifies the function that creates an object's prototype. Note that the value of this property is a reference to the function itself, not a string containing the function's name.
Property of |
Array |
Implemented in |
JavaScript 1.1, NES 2.0 |
ECMA version |
ECMA-262 |
Description
See Object.constructor.
index
For an array created by a regular expression match, the zero-based index of the match in the string.
Property of |
Array |
Static |
|
Implemented in |
JavaScript 1.2, NES 3.0 |
input
For an array created by a regular expression match, reflects the original string against which the regular expression was matched.
Property of |
Array |
Static |
|
Implemented in |
JavaScript 1.2, NES 3.0 |
join
Joins all elements of an array into a string.
Method of |
Array |
Implemented in |
JavaScript 1.1, NES 2.0 |
ECMA version |
ECMA-262 |
Syntax
join(separator)
Parameters
separator
|
Specifies a string to separate each element of the array. The separator is converted to a string if necessary. If omitted, the array elements are separated with a comma. |
Description
The string conversions of all array elements are joined into one string.
Examples
The following example creates an array, a, with three elements, then joins the array three times: using the default separator, then a comma and a space, and then a plus.
a = new Array("Wind","Rain","Fire")
myVar1=a.join()// assigns "Wind,Rain,Fire" to myVar1
myVar2=a.join(", ")// assigns "Wind, Rain, Fire" to myVar1
myVar3=a.join(" + ")// assigns "Wind + Rain + Fire" to myVar1
See also
Array.reverse
length
An unsigned, 32-bit integer that specifies the number of elements in an array.
Property of |
Array |
Implemented in |
JavaScript 1.1, NES 2.0
JavaScript 1.3: length is an unsigned, 32-bit integer with a value less than 232. |
ECMA version |
ECMA-262 |
Description
The value of the length property is an integer with a positive sign and a value less than 2 to the 32 power (232).
You can set the length property to truncate an array at any time. When you extend an array by changing its length property, the number of actual elements does not increase; for example, if you set length to 3 when it is currently 2, the array still contains only 2 elements.
Examples
In the following example, the getChoice function uses the length property to iterate over every element in the musicType array. musicType is a select element on the musicForm form.
function getChoice() {
for (var i = 0; i < document.musicForm.musicType.length; i++) {
if (document.musicForm.musicType.options[i].selected == true) {
return document.musicForm.musicType.options[i].text
}
}
}
The following example shortens the array statesUS to a length of 50 if the current length is greater than 50.
if (statesUS.length > 50) {
statesUS.length=50
}
pop
Removes the last element from an array and returns that element. This method changes the length of the array.
Method of |
Array |
Implemented in |
JavaScript 1.2, NES 3.0 |
ECMA version |
ECMA-262 Edition 3 |
Syntax
pop()
Parameters
None.
Example
The following code creates the myFish array containing four elements, then removes its last element.
myFish = ["angel", "clown", "mandarin", "surgeon"];
popped = myFish.pop();
See also
push, shift, unshift
prototype
Represents the prototype for this class. You can use the prototype to add properties or methods to all instances of a class. For information on prototypes, see Function.prototype.
Property of |
Array |
Implemented in |
JavaScript 1.1, NES 2.0 |
ECMA version |
ECMA-262 |
push
Adds one or more elements to the end of an array and returns the new length of the array. This method changes the length of the array.
Method of |
Array |
Implemented in |
JavaScript 1.2, NES 3.0
JavaScript 1.3: push returns the new length of the array rather than the last element added to the array. |
ECMA version |
ECMA-262 Edition 3 |
Syntax
push(element1, ..., elementN)
Parameters
element1, ..., elementN
|
The elements to add to the end of the array. |
Description
The behavior of the push method is analogous to the push function in Perl4. Note that this behavior is different in Perl5.
Backward Compatibility
JavaScript 1.2. The push method returns the last element added to an array.
Example
The following code creates the myFish array containing two elements, then adds two elements to it. After the code executes, pushed contains 4. (In JavaScript 1.2, pushed contains "lion" after the code executes.)
myFish = ["angel", "clown"];
pushed = myFish.push("drum", "lion");
See also
pop, shift, unshift
reverse
Transposes the elements of an array: the first array element becomes the last and the last becomes the first.
Method of |
Array |
Implemented in |
JavaScript 1.1, NES 2.0 |
ECMA version |
ECMA-262 |
Syntax
reverse()
Parameters
None
Description
The reverse method transposes the elements of the calling array object.
Examples
The following example creates an array myArray, containing three elements, then reverses the array.
myArray = new Array("one", "two", "three")
myArray.reverse()
This code changes myArray so that:
-
myArray[0] is "three"
-
myArray[1] is "two"
- myArray[2] is "one"
See also
Array.join, Array.sort
shift
Removes the first element from an array and returns that element. This method changes the length of the array.
Method of |
Array |
Implemented in |
JavaScript 1.2, NES 3.0 |
ECMA version |
ECMA-262 Edition 3 |
Syntax
shift()
Parameters
None.
Example
The following code displays the myFish array before and after removing its first element. It also displays the removed element:
myFish = ["angel", "clown", "mandarin", "surgeon"];
document.writeln("myFish before: " + myFish);
shifted = myFish.shift();
document.writeln("myFish after: " + myFish);
document.writeln("Removed this element: " + shifted);
This example displays the following:
myFish before: ["angel", "clown", "mandarin", "surgeon"]
myFish after: ["clown", "mandarin", "surgeon"]
Removed this element: angel
See also
pop, push, unshift
slice
Extracts a section of an array and returns a new array.
Method of |
Array |
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