Question

I’m unable to get the length of the following JSON array object. Actually I need to return the values of the penultimate array elements.

var myObject = { "Maths" : [{"Name" : "Amit", "Marks" : 67, "age" : 23 },
{"Name"  : "Sandeep", "Marks" : 65, "age" : 21 },
{"Name"  : "Shali", "Marks" : 56, "age" : 27 },  
{"Name"  : "Santosh", "Marks" : 78, "age" : 41 }] }

a = myObject.Maths.length - 1;
alert(a);
var b=new Object();
b.mk=myObject.Maths[a]['Marks'];
b.ag=myObject.Maths[a]['age'];
alert(b.mk);
alert(b.ag);

Why is this returning 78 and 41 when it should return 56 and 27?

Answer 1

Why do you think it would return 56 and 27? Do you realize array indexes start at 0?
So if a = 3 (length – 1, 4 – 1 = 3).

the third index of the Math’s array is exactly what you are seeing in the output.

edit: so, in order to get the penultimate, your index would need to be length – 2. (of course making sure you array is actually long enough to not run into an out of bounds error)