++variable vs variable++

Hi all,

I’m reading Sitepoint’s Simply JavaScript at the moment and am a bit confused by some information on page 26.

Here, Cameron Adams is trying to explain the difference between:

var age=26;
var ageCopy = age++;


var age=26;
var ageCopy = ++age;

He says that in the first example, ageCopy is equal to 26, but in the second example, ageCopy == 27.

I don’t understand this - isn’t ageCopy equal to 27 in both of these examples? What is the actual difference between these statements?


ageCopy = age++ - increments and then assigns

ageCopy = ++age - assigns and then increments

In both cases age ends up as 27 but not ageCopy

ORLY? Are you sure it isn’t the other way around? :wink:

Sorry got that completely the wrong way around

ageCopy = age++ - assigns and then increments

ageCopy = ++age - increments and then assigns


var a = 1;
alert(a++); // alerts 1

var a = 1;
alert(++a); // alerts 2

++var is only ever needed in some very special cases. var++ will suffice for 99,99% of the cases where you need to increment a variable :slight_smile:

The Major difference between ++a , a++ is the manner of increment and assignment.

in first case agecopy=age++
let the value of age is 26
in that case agecopy first assigns the non incremented value if age.
later compiler increments the age value to 1 and the final age value
becomes 27

in second case agecopy=++age
let the value of age is 26
now compiler increment the value of age to 1 and final age value becomes
later it compiler assigns the incremented value to agevalue.
and ultimately agevalue becomes 27.

I had the same problem the first time I read that in Simply Javascript.

I think it’s a badly-done example. If he had added some more code afterwards, it would have been clearer.

Yeah, I agree with you - it could do with a few extra lines of explanation.

Thanks for the help everyone, I understand it now. :slight_smile: