Common uses for JavaScript arrays

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Defining arrays An array object is used to store a series of values in a separate variable name. We use the keyword new to create an array object. The following code defines an array object named MyArray: The Var myarray=new array () has two methods of assigning values to an array (you can add as many values as you want, as you can define any number of variables you need). 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 ([element0[, element1[, ...)　[, ELEMENTN]]]); Create an array and assign a value Note: If you need to specify numeric or logical values within an array, the variable type should be either a numeric variable or a Boolean variable, not a character variable. accessing arrays You can access a particular element by specifying the array name and the index number. Here is the line of code: document.write (Mycars[0]) below is the output: Saab modifies the values in an existing array If you want to modify the values in an existing array, add a new value to the specified bottom label: Mycars[0]= "Opel"; now, the above code: document.write (mycars[0]); output: 2, access to elements of the array var testgetarrvalue=arrayobj[1]; Gets the element value of an array Arrayobj[1]= "This is the new value"; Give a new value to an array element 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 the new length of the array 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 (); 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 ([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 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=[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]; 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 { function body. } y = new MyFunc; if (Y.constructor = = MyFunc)//To be processed (condition is true). Merging arrays <body> <script type= "Text/javascript" > var arr = new Array (3) Arr[0] = "George" ARR[1] = "John" ARR[2] = "Thomas" var arr2 = new Array (3) Arr2[0] = "James" ARR2[1] = "Adrew" ARR2[2] = "Martin" document.write (Arr.concat (ARR2)) </script> </body> <body> Merging two arrays-concat () How to use the Concat () method to merge two arrays. <script type= "Text/javascript" > var arr = new Array (3); Arr[0] = "George" ARR[1] = "John" ARR[2] = "Thomas" document.write (Arr.join ()); document.write ("<br/>"); document.write (Arr.join (".")); </script> </body> Composition string with elements of an array-join () How to use the Join () method to make all the elements of an array a string. <body> <script type= "Text/javascript" > var arr = new Array (3); Arr[0] = "George" ARR[1] = "John" ARR[2] = "Thomas" document.write (Arr.join ()); document.write ("<br/>"); document.write (Arr.join (".")); </script> </body> Type array-sort () How to use the sort () method to literally sort the array. <script type= "Text/javascript" > var arr = new Array (6) Arr[0] = "George" ARR[1] = "John" ARR[2] = "Thomas" ARR[3] = "James" ARR[4] = "Adrew" ARR[5] = "Martin" document.write (arr + "<br/>") document.write (Arr.sort ()) </script> Array of numbers-sort () How to use the sort () method to sort the array on a numeric value. <script type= "Text/javascript" > function Sortnumber (A, B) { Return A-b } var arr = new Array (6) Arr[0] = "10" ARR[1] = "5" ARR[2] = "40" ARR[3] = "25" Arr[4] = "1000" ARR[5] = "1" document.write (arr + "<br/>") document.write (Arr.sort (Sortnumber)) </script>