JS basics
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Introduction
Alongside with HTML and CSS, JavaScript is one of the essential technologies of web documents. It is the one that makes the app interactable.
Datatypes
In JavaScript there are 6 primitive datatypes.
Undefined
A variable that has not been assigned a value has the value undefined.
Null
The Null type has exactly one value: null. It refers to the absence of a value.
Boolean
Boolean represents a logical entity and can have two values: true and false.
Number
Number represents numeric values eg: 11
String
It is used to represent textual data. eg: 'Hey developer'
Symbol
A Symbol is a unique and immutable primitive value and may be used as the key of an Object property.
Objects
Objects are nothing but an informtaion or data. These are the foundation of JavaScript. In JavaScript, an object can be thought of as a distinct entity that can have properties associated with it. These properties define the object’s characteristics and behavior.
Events
Events are actions or occurence that happen in the system.For example, clicking a button or pressing a key are events. We can use JavaScript to execute code in response of these events. Every HTML contains a set of events which can trigger JavaScript code.
onclick
It is a mouse event that occurs when a user clicks on a button (or any element). We can add a logic against this event type.
<!doctype html><html><head><script>function submit() {alert('Button clicked');}</script></head><body><button type="button" onclick="submit()">Click me</button></body></html>
In the above example, when a user clicks on the button Click me, then a function defined for the onclick event(submit()) is executed.
onsubmit
This event occurs when we submit a form.
Onmouseover
This event triggers when we hover the mouse pointer on any element.
onfocus
This event triggers when an element gets focus.