What is a constructor method ?
This is a method used to create and initialise a javascript object.
Whenever the memory is allocated for javascript object constructor method is called.
How to create constructor method ?
“constructor” keyword is used to declare a constructor method.
Javascript class can contain only one constructor method.
Parent class constructor can be accessed by using “super” keyword.
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Syntax :
constructor(argument1,argument2,argument3...argumentN);
1. Simple Constructor inside a class
Example :
<script>
class StudentInfo{
constructor(name,age,address)
{
this.name = name;
this.age = age;
this.address = address;
}
}
var a = new StudentInfo("Abdul","33","Chennai");
document.writeln("Name = " + a.name+"<br/>");
document.writeln("Age = " + a.age+"<br/>");
document.writeln("Address = " + a.address+"<br/>");
</script>
Output :
2. Constructor with “super” keyword.
Suppose we have a main class “StudentInfo” and sub class “StudentMarksInfo”.
Example :
<script>
class StudentInfo{
constructor()
{
this.name = "Abdul";
this.age = "14";
this.address = "Chennai";
}
}
class StudentMarksInfo extends StudentInfo{
constructor(english,tamil,maths,science,biology,history,geography){
super();
this.english = english;
this.tamil = tamil;
this.maths = maths;
this.science = science;
this.biology = biology;
this.history = history;
this.geography = geography;
}
}
var b = new StudentMarksInfo("87","99","100","98","87","100","77");
document.writeln("Name = " + b.name+"<br/>");
document.writeln("Age = " + b.age+"<br/>");
document.writeln("Address = " + b.address+"<br/>");
document.writeln("English Mark = " + b.english+"<br/>");
document.writeln("Tamil Mark = " + b.tamil+"<br/>");
document.writeln("Maths Mark = " + b.maths+"<br/>");
document.writeln("Science Mark = " + b.science+"<br/>");
document.writeln("Biology Mark = " + b.biology+"<br/>");
document.writeln("History Mark = " + b.history+"<br/>");
document.writeln("Geography Mark = " + b.geography+"<br/>");
</script>
Output :
