Introduction to JS Array object analysis_javascript skills

However, in the process of learning the script prototype.js, I found that there are some methods that we rarely use, but some methods seem to be very classic. The script library is constantly increasing, and everything in front of us... Let's continue our introduction to JS and learn about Array arrays today.
First let’s take a look at its definition:

Copy the code The code is as follows:

var arrayObj = new Array()
var arrayObj = new Array([size])
var arrayObj = new Array([element0[, element1[, [, elementN]]]])

Where: arrayObj is the variable name assigned to the Array object.
size Since array subscripts start from zero, the subscripts of the created elements will be from zero to size -1.
element0,...,elementN This creates an array of length n 1 with n 1 elements. More than one element is required to use this syntax.
If only one argument is passed to Array's constructor, and that argument is a number, it must be an unsigned 32-bit integer (approximately 4 billion). This value becomes the size of the array. If the value is numeric but less than 0 or not an integer, a runtime error occurs.
If the value passed to the Array constructor is a single value and not a numeric value, the length property is set to 1 and the unique element value becomes the single passed-in parameter.
Since JS arrays are parsed arrays, that is, although multiple elements can be assigned to an array, only the elements containing data actually exist. This reduces the amount of memory used by the array.
The Array object has three built-in properties: constructor, length, prototype. I will write a special article about constructor, prototype, arguments and other object properties, so I won’t go into details here. Below we mainly look at some of the built-in methods of Array. This is very important to us because we will use this stuff frequently.
concat method: concatenates two or more arrays and returns a new array. It is worth noting that (reference type) the object parameters copied from the array being connected to the new array still point to the same object after copying. No matter which one of the new array and the source array is changed, the other will be caused. Change; (value type) For the numerical value or string connected to the new array, only its value is copied. Changes in the value in one array do not affect the value in the other array. Example:

Copy code The code is as follows:

1 function ConcatArrayDemo(){
2 var a, b, c, d;
3 a = new Array(1,2,3);
4 b = "JScript";
5 c = new Array(42, "VBScript);
6 d = a.concat(b, c);
7 // Return array [1, 2, 3, "JScript", 42, "VBScript"]
8 return(d);
9 }
10

join method: Convert the items in the array into a string according to a specific delimiter and return it. The default delimiter is comma, example:

Copy code The code is as follows:

1 function JoinDemo(){
2 var a, b;
3 a = new Array(0,1,2,3,4);
4 b = a.join("-");
5 //Return: "0-1-2-3 -4"
6 return(b);
7 }

pop method: removes the last element in the array and returns the element. Returns if the array is empty undefined.
push method: will add the new elements in the order they appear, if one of the parameters is an array, then the array will be added to the array as a single element if you want to merge elements from two or more arrays. , please use the concat method. The
reverse method reverses the position of elements in an Array object. During execution, this method does not create a new Array object. If the array is discontinuous, the reverse method will. Create elements in an array to fill the gaps in the array. The values ​​of all the elements created are undefined. The code is as follows:

1 function ReverseDemo(){ 2 var a, l; // Declare variables. 3 a = new Array(0,1,2,3,4. ); // Create an array and assign a value. 4 l = a.reverse(); // Reverse the contents of the array. 5 // Return: l=[4,3,2,1,0]. 6 return(l); // Return the result array.

7 }

The shift method removes the first element in an array and returns that element.
The slice method returns an Array object, which contains the specified part of arrayObj. The slice method copies up to, but not including, the element specified by end. If start is negative, treat it as length start, where length is the length of the array. If end is negative, it is treated as length end, where length is the length of the array. If end is omitted, the slice method copies until the end of arrayObj. If end appears before start, no elements are copied to the new array. Example:
//Except for the last element, all elements in myArray are copied to newArray:
newArray = myArray.slice(0, -1)
The sort method sorts the Array object appropriately Sorting; no new Array objects are created during execution. If a function is provided for the sortfunction argument, the function must return one of the following values:
· Negative value if the first argument passed is smaller than the second argument.
· Zero if both parameters are equal.
· Positive value if the first parameter is larger than the second parameter.

Copy code The code is as follows:

1 function SortDemo(){
2 var a , l; // Declare variables.
3 a = new Array("X" ,"y" ,"d", "Z", "v","m","r");
4 l = a.sort(); // Sort the array.
5 return(l); // Return the sorted array.
6 }

The splice method can modify arrayObj by removing a specified number of elements starting from the start position and inserting new elements. The return value is a new Array object consisting of the removed elements. The format is as follows:
arrayObj.splice(start, deleteCount, [item1[, item2[, . . . [,itemN]]]])
toLocaleString method will be explained in the Date object. Generally, this method just returns to User, not calculated as in code. The
unshift method inserts the elements at the beginning of an array, so they appear in the array in the order in which the arguments are sequenced. The format is as follows:
arrayObj.unshift([item1[, item2 [, . . . [, itemN]]]])
valueOf method&toString() The elements of the array are converted to strings, which are separated by commas Separate, connect together. Its operation is the same as the Array.toString and Array.join methods.