An introductory tutorial on Javascript array usage

Defining arrays

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var a = new Array ("A", "B", "C"); Method 1. var mycars=new Array () mycars[0]= "Saab" mycars[1]= "Volvo" mycars[2]= "BMW"

Method 2.

Define and initialize together:

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var mycars=new Array ("Saab", "Volvo", "BMW")

Or another way of writing:

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var mycars=["Saab", "Volvo", "BMW"];

Looping Read

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for (i = 0; i < a.length i++) {//circular read document.write (i + ":" + a[i] + "<br/>"); } document.write ("toString ():" + a.tostring () + "<br/>");//tostring (), array in string representation document.write ("Join ():" + A.join ("") + "<br/>");//join (), with the string argument after the join as the spacer, generates a string, if the argument is a half-width comma, the effect and ToString ( ) The same document.write ("reverse ():" + a.reverse (). toString () + "<br/>"); Generate a new array of elements in the array in reverse document.write ("valueof ():" + a.valueof () + "<br/>");//valueof (), Output array value

Two-dimensional array

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var b = new Array (3);//define an array of length 3 B[0] = new Array ("a", 1); B[1] = new Array ("B", 2); B[2] = new Array ("C", 3); for (i = 0; i < b.length; i++) {//loop output each element of each dimension for (j = 0; J < B[i].length; J + +) { document.write ("b[" + i + "] [" + j + "]:" + b[i][j] + "<br/>"); } }

Array Length:

The JavaScript array does not need to be set in length, it expands itself, and the array name. Length returns the number of elements

The following is an example of changing the length property:

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var arr=[ 12,23,5,3,25,98,76,54,56,76]; //defines a 10-digit array alert (arr.length); //Displays the length of the array arr.length=12;  //increase the length of the array alert ( Arr.length); //display the length of the array has changed to Alert (arr[8]);  //Display the value of the 9th element, 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]);  //display 9th element has changed to "undefined" arr.length=10;   //restore array length to 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:

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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.

Attached message:
Supnate: There is no specific example, and it is understood that the length property understands the array in JavaScript. Arrays are the basis for many examples. Because it is quite different from other languages, so speak it alone. For example, to implement a pop method for arrays that are not supported by a low version browser:

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Array.prototype.pop=function () { if (0==this.length) return; var temp=this[this.length-1]; this.length--; return temp; }

So the array can be used as a stack.