Sunday, September 22, 2019
Introduction to JavaScript Arrays
Arrays are a means of creating a collection of values of the same kind by javascript.A type of value means either only strings or only integers or floating point numbers etc. Arrays are used to avoid the problem of creating too many variables.
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| JavaScript Arrays |
For example, if you want to store the names of 200 employees, for that you do not need to create 200 variables. You can create an array in which 200 names can be stored. Doing this saves the time of programmers.
Array Elements Indexing in JavaScript
Every element of an array can be uniquely identified. Stores the array values by indexing. But always remember that the array starts with index zero.So in the example mentioned above, the first name will be at 0 index and finally the name will be at 199 index. You can access any value of an array by the name of the array and its index number. You should also always remember that arrays are objects in JavaScript. That's why you create them by new keyword.
Although JavaScript also provides you the option to put values directly but still arrays objects remain in JavaScript.
Creating JavaScript Arrays
Arrays can be created in JavaScript in 2 ways. Both these methods can be used according to different situation.- Directly - In this method you create an array and also add value. This is a combined way to create an array.
- With new keyword - In this way you create the array as an object. In this method, first the array is created and later values can be inserted. If you want, you can also add values together for this, you use the constructor of the array object.
Both methods can be used in different situations according to the need.
Directly (Combined Way)
Creating an array in this way is very simple.Syntax
var array_Name = [value1, value2, ..... valueN];In this method, the name of the array is written after the var keyword. Array's name must be unique. Array values are given in angular brackets by placing an assignment operator after the name of the array. Values are separated from comma.
Example1: Creating & initializing array
<html>
<head>
<title> Javascript array demo </title>
</head>
<body>
<script type = "text / javascript">
// Array declaration
var empName = ["Sam", "Sally", "Tina", "Raghav", "John"];
// Printing array elements
for (i = 0; i <5; i ++)
{
document.write (empName [i], "n");
}
</script>
</body>
</html>
With New Keyword
In this way, you use the new keyword to create an array in javascript. This is similar to creating an object.Syntax
var array_Name = new Array ();
array_Name [0] = value1;
array_Name [1] = value2;
...
...
array_Name [n] = valueN;
If you want to add values as well, then you can create an array from the structure given below.
var array_Name = new Array (value1, value2);
In the above method first array is created followed by values by index numbers. In the following method the values are put by the constructor of the Array object.
These values constructor automatically assigns index numbers.
Example2: Array with new keyword
<html>
<head>
<title> Javascript new keyword demo </title>
</head>
<body>
<script type = "text / javascript">
// Array declaration using new keyword
var empName = new Array ("Angelina", "Sam");
// Printing array elements
for (i = 0; i <2; i ++)
{
document.write (empName [i]);
}
</script>
</body>
</html>
JavaScript Arrays Length Property
JavaScript provides you with length property with array object. This property holds the length of your array.Syntax
array_Name.length;If you want, you can use this property to do loop control.
Example3: Loop to array length
<script type = "text / javascript">
var empAge = new Array (24,42,21,55,23,30);
// Displaying length of array
document.write ("Length of array is" + empAge.length);
// Iterating loop upto array length
for (var i = 0; i <empAge.length; i ++)
{
document.write (empAge [i]);
}
</script>