Javascript Generate Dynamic Key Values In An Object
JavaScript is designed on a simple object-based paradigm. An object is a collection of properties, and a property is an association between a name (or key) and a value. A property's value can be a function, in which case the property is known as a method. In addition to objects that are predefined in the browser, you can define your own objects. Object.keys is used for returning enumerable properties of an array like object. Object.keys is used for returning enumerable properties of an array like object with random key ordering. Syntax: Object.keys(obj) Parameters Used: obj: It is the object whose enumerable properties are to be returned. Return Value: Object.keys returns an.
- Javascript Variable As Key
- Javascript Dynamic String
- Javascript Generate Dynamic Key Values In An Object Examples
JSON is a format for storing and transporting data.
Likewise, you cannot compare someone like me or you as performing this scenario, as it wouldn't be.As for viewing, you won't be able to view the.cof file with a program like notepad. They'll still need to be extracted from the MPQ file, and then re-inserted back into the new one. So you're talking about just moving the.wav and the.cof files? Sure, it's not an overly difficult task, but it would still involve an MPQ viewer, which I do class as a special program. Diablo 2 multiplayer cd key generator.
JSON is often used when data is sent from a server to a web page.
What is JSON?
- JSON stands for JavaScript Object Notation
- JSON is a lightweight data interchange format
- JSON is language independent *
- JSON is 'self-describing' and easy to understand
* The JSON syntax is derived from JavaScript object notation syntax, but the JSON format is text only. Code for reading and generating JSON data can be written in any programming language.
JSON Example
This JSON syntax defines an employees object: an array of 3 employee records (objects):
JSON Example
'employees':[
{'firstName':'John', 'lastName':'Doe'},
{'firstName':'Anna', 'lastName':'Smith'},
{'firstName':'Peter', 'lastName':'Jones'}
]
}
The JSON Format Evaluates to JavaScript Objects
The JSON format is syntactically identical to the code for creating JavaScript objects.
Because of this similarity, a JavaScript program can easily convert JSON data into native JavaScript objects.
JSON Syntax Rules
- Data is in name/value pairs
- Data is separated by commas
- Curly braces hold objects
- Square brackets hold arrays
JSON Data - A Name and a Value
JSON data is written as name/value pairs, just like JavaScript object properties.
A name/value pair consists of a field name (in double quotes), followed by a colon, followed by a value:
JSON names require double quotes. JavaScript names do not.
JSON Objects
JSON objects are written inside curly braces.
Just like in JavaScript, objects can contain multiple name/value pairs:
JSON Arrays
JSON arrays are written inside square brackets.
Just like in JavaScript, an array can contain objects:
{'firstName':'John', 'lastName':'Doe'},
{'firstName':'Anna', 'lastName':'Smith'},
{'firstName':'Peter', 'lastName':'Jones'}
]
In the example above, the object 'employees' is an array. It contains three objects.
Each object is a record of a person (with a first name and a last name).
Converting a JSON Text to a JavaScript Object
A common use of JSON is to read data from a web server, and display the data in a web page.
For simplicity, this can be demonstrated using a string as input.
First, create a JavaScript string containing JSON syntax:
'{ 'firstName':'John' , 'lastName':'Doe' },' +
'{ 'firstName':'Anna' , 'lastName':'Smith' },' +
'{ 'firstName':'Peter' , 'lastName':'Jones' } ]}';
Then, use the JavaScript built-in function JSON.parse() to convert the string into a JavaScript object:
Finally, use the new JavaScript object in your page:
Example
<script>
document.getElementById('demo').innerHTML =
obj.employees[1].firstName + ' ' + obj.employees[1].lastName;
</script>
You can read more about JSON in our JSON tutorial.
JavaScript arrays are used to store multiple values in a single variable.
Example
Try it Yourself »What is an Array?
An array is a special variable, which can hold more than one value at a time.
If you have a list of items (a list of car names, for example), storing the cars in single variables could look like this:
var car2 = 'Volvo';
var car3 = 'BMW';
However, what if you want to loop through the cars and find a specific one? And what if you had not 3 cars, but 300?
The solution is an array!
An array can hold many values under a single name, and you can access the values by referring to an index number.
Creating an Array
Using an array literal is the easiest way to create a JavaScript Array.
Syntax:
Example
Try it Yourself »Spaces and line breaks are not important. A declaration can span multiple lines:
Example
Try it Yourself »Using the JavaScript Keyword new
The following example also creates an Array, and assigns values to it:
Example
Try it Yourself »The two examples above do exactly the same. There is no need to use new Array().
For simplicity, readability and execution speed, use the first one (the array literal method).
Access the Elements of an Array
You access an array element by referring to the index number.
This statement accesses the value of the first element in cars:
Example
document.getElementById('demo').innerHTML = cars[0];
Note: Array indexes start with 0.
[0] is the first element. [1] is the second element.
Changing an Array Element
This statement changes the value of the first element in cars:
Example
cars[0] = 'Opel';
document.getElementById('demo').innerHTML = cars[0];
Access the Full Array
With JavaScript, the full array can be accessed by referring to the array name:
Example
document.getElementById('demo').innerHTML = cars;
Arrays are Objects
Arrays are a special type of objects. The typeof operator in JavaScript returns 'object' for arrays.
But, JavaScript arrays are best described as arrays.
Arrays use numbers to access its 'elements'. In this example, person[0] returns John:
Array:
Try it Yourself »Objects use names to access its 'members'. In this example, person.firstName returns John:
Object:
Array Elements Can Be Objects
JavaScript variables can be objects. Arrays are special kinds of objects.
Because of this, you can have variables of different types in the same Array.
You can have objects in an Array. You can have functions in an Array. You can have arrays in an Array:
myArray[1] = myFunction;
myArray[2] = myCars;
Array Properties and Methods
The real strength of JavaScript arrays are the built-in array properties and methods:
Examples
var y = cars.sort(); // The sort() method sorts arrays
Array methods are covered in the next chapters.
The length Property
The length property of an array returns the length of an array (the number of array elements).
Example
fruits.length; // the length of fruits is 4
The length property is always one more than the highest array index.
Accessing the First Array Element
Example
var first = fruits[0];
Accessing the Last Array Element
Example
var last = fruits[fruits.length - 1];
Looping Array Elements
The safest way to loop through an array, is using a for loop:
Example
fruits = ['Banana', 'Orange', 'Apple', 'Mango'];
fLen = fruits.length;
text = '<ul>';
for (i = 0; i < fLen; i++) {
text += '<li>' + fruits[i] + '</li>';
}
text += '</ul>';
You can also use the Array.forEach() function:
Example
fruits = ['Banana', 'Orange', 'Apple', 'Mango'];
text = '<ul>';
fruits.forEach(myFunction);
text += '</ul>';
function myFunction(value) {
text += '<li>' + value + '</li>';
}
Adding Array Elements
The easiest way to add a new element to an array is using the push() method:
Example
fruits.push('Lemon'); // adds a new element (Lemon) to fruits
New element can also be added to an array using the length property:
Example
fruits[fruits.length] = 'Lemon'; // adds a new element (Lemon) to fruits
WARNING !
Adding elements with high indexes can create undefined 'holes' in an array:
Example
fruits[6] = 'Lemon'; // adds a new element (Lemon) to fruits
Associative Arrays
Many programming languages support arrays with named indexes.
Arrays with named indexes are called associative arrays (or hashes).
JavaScript does not support arrays with named indexes.
In JavaScript, arrays always use numbered indexes.
Example
person[0] = 'John';
person[1] = 'Doe';
person[2] = 46;
var x = person.length; // person.length will return 3
var y = person[0]; // person[0] will return 'John'
WARNING !!
If you use named indexes, JavaScript will redefine the array to a standard object.
After that, some array methods and properties will produce incorrect results.
Example:
person['firstName'] = 'John';
person['lastName'] = 'Doe';
person['age'] = 46;
var x = person.length; // person.length will return 0
var y = person[0]; // person[0] will return undefined
The Difference Between Arrays and Objects
In JavaScript, arrays use numbered indexes.
In JavaScript, objects use named indexes.
Arrays are a special kind of objects, with numbered indexes.
When to Use Arrays. When to use Objects.
- JavaScript does not support associative arrays.
- You should use objects when you want the element names to be strings (text).
- You should use arrays when you want the element names to be numbers.
Avoid new Array()
There is no need to use the JavaScript's built-in array constructor new Array().
Use [] instead.
These two different statements both create a new empty array named points:
var points = []; // Good
These two different statements both create a new array containing 6 numbers:
var points = [40, 100, 1, 5, 25, 10]; // Good
The new keyword only complicates the code. It can also produce some unexpected results:
What if I remove one of the elements?
How to Recognize an Array
Javascript Variable As Key
A common question is: How do I know if a variable is an array?
The problem is that the JavaScript operator typeof returns 'object':
typeof fruits; // returns object
The typeof operator returns object because a JavaScript array is an object.
Solution 1:
To solve this problem ECMAScript 5 defines a new method Array.isArray():
The problem with this solution is that ECMAScript 5 is not supported in older browsers.
Solution 2:
Javascript Dynamic String
To solve this problem you can create your own isArray() function:
return x.constructor.toString().indexOf('Array') > -1;
}
The function above always returns true if the argument is an array.
Or more precisely: it returns true if the object prototype contains the word 'Array'.
Solution 3:
The instanceof operator returns true if an object is created by a given constructor:
fruits instanceof Array; // returns true