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SCRIPT5007: Unable to get property '0' of undefined or null reference

Posted on 2014-12-19
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Last Modified: 2014-12-20
Why do I get an error on this line?  "SCRIPT5007: Unable to get property '0' of undefined or null reference "
            console.log("Class 1: "+newStudent.Classes[0]);

		function student(firstName,lastName,ssn,dormName)
		{
			this.fname = firstName;
			this.lname = lastName;
			this._ssn = ssn || 0;
			this.classes = [];
			this.dName = dormName || "A Hall";
		};
		
		// Individually add methods to the prototype
		student.prototype.addClasses = function(className, roomNumber) {
			this.classes.push({className: className, roomNumber: roomNumber});
		};

		Object.defineProperty(student.prototype, "fullname", {
			get: function() {
				return this.fname + " " + this.lname;
			}
		});
		
		var newStudent = new student("John","Doe","231-31-1313","jjjjj1111");
		console.log("HELLO WORLD");
		console.log(newStudent.fullname);
		newStudent.addClasses("Algebra", "33B");
		newStudent.addClasses("Geometry", "44B");
		newStudent.addClasses("History", "12B");
		newStudent.addClasses("Sociology", "144C");
		newStudent.addClasses("Biology", "312D");
		newStudent.addClasses("Calculus", "98S");
		newStudent.addClasses("Statistics", "55B");
		
		console.log("Number of classes: " + newStudent.classes.length);
		console.log("Class 1: "+newStudent.Classes[0]);

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Question by:Isaac
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5 Comments
 
LVL 6

Accepted Solution

by:
oferam earned 1400 total points
ID: 40510405
It's case sensitive - "console.log("Class 1: "+newStudent.Classes[0])" should be console.log("Class 1: "+newStudent.classes[0])
0
 
LVL 5

Author Comment

by:Isaac
ID: 40510406
The error is gone but now the console renders "Class 1: [object Object] "
0
 
LVL 6

Expert Comment

by:oferam
ID: 40510420
That's another question :)

I guess it's because it does not recognize the object you've inserted.

try printing newStudent.classes[0].className - to get the class name and roomNumber to get the room number
0
 
LVL 84

Assisted Solution

by:Dave Baldwin
Dave Baldwin earned 600 total points
ID: 40510474
Out of curiosity, I made a web page out of your code and @oferam is right, you needed to 'name' the objects to get them to appear.  How are you seeing the response in the 'console'?
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
 "http://www.w3.org/TR/html4/loose.dtd">

<html>
<head>
<title>JS Classes</title>
</head>
<body>
<h1>JS Classes</h1>
<script type="text/javascript">
<!--
		function student(firstName,lastName,ssn,dormName)
		{
			this.fname = firstName;
			this.lname = lastName;
			this._ssn = ssn || 0;
			this.classes = [];
			this.dName = dormName || "A Hall";
		};
		
		// Individually add methods to the prototype
		student.prototype.addClasses = function(className, roomNumber) {
			this.classes.push({className: className, roomNumber: roomNumber});
		};

		Object.defineProperty(student.prototype, "fullname", {
			get: function() {
				return this.fname + " " + this.lname;
			}
		});
		
		var newStudent = new student("John","Doe","231-31-1313","jjjjj1111");
		console.log("HELLO WORLD");
		console.log(newStudent.fullname);
		newStudent.addClasses("Algebra", "33B");
		newStudent.addClasses("Geometry", "44B");
		newStudent.addClasses("History", "12B");
		newStudent.addClasses("Sociology", "144C");
		newStudent.addClasses("Biology", "312D");
		newStudent.addClasses("Calculus", "98S");
		newStudent.addClasses("Statistics", "55B");
		
		console.log("Number of classes: " + newStudent.classes.length);
		document.write("Number of classes: " + newStudent.classes.length + "<br>");
		console.log("Class 1: "+newStudent.classes[0]);
		document.write("Class 1: "+newStudent.classes[0].className+" "+newStudent.classes[0].roomNumber);

// -->
</script>
</body>
</html>

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LVL 84

Expert Comment

by:Dave Baldwin
ID: 40510477
And to list all of the classes...
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
 "http://www.w3.org/TR/html4/loose.dtd">

<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<title>JS Classes</title>
</head>
<body>
<h1>JS Classes</h1>
<script type="text/javascript">
<!--
		function student(firstName,lastName,ssn,dormName)
		{
			this.fname = firstName;
			this.lname = lastName;
			this._ssn = ssn || 0;
			this.classes = [];
			this.dName = dormName || "A Hall";
		};
		
		// Individually add methods to the prototype
		student.prototype.addClasses = function(className, roomNumber) {
			this.classes.push({className: className, roomNumber: roomNumber});
		};

		Object.defineProperty(student.prototype, "fullname", {
			get: function() {
				return this.fname + " " + this.lname;
			}
		});
		
		var newStudent = new student("John","Doe","231-31-1313","jjjjj1111");
		console.log("HELLO WORLD");
		console.log(newStudent.fullname);
		newStudent.addClasses("Algebra", "33B");
		newStudent.addClasses("Geometry", "44B");
		newStudent.addClasses("History", "12B");
		newStudent.addClasses("Sociology", "144C");
		newStudent.addClasses("Biology", "312D");
		newStudent.addClasses("Calculus", "98S");
		newStudent.addClasses("Statistics", "55B");
		
		console.log("Number of classes: " + newStudent.classes.length);
		document.write("Number of classes: " + newStudent.classes.length + "<br>");
		for(var ii=0;ii<newStudent.classes.length;ii++) {
		console.log("Class "+(ii+1)+": "+newStudent.classes[ii]);
		document.write("Class "+(ii+1)+": "+newStudent.classes[ii].className+" "+newStudent.classes[ii].roomNumber + "<br>");
		}

// -->
</script>
</body>
</html>

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