Weird Code - Dynamic properties in primitive and reference variables in javascript (JS) -

Weird Code - Dynamic properties in primitive and reference variables in javascript (JS) -

i'm working through learning javascript , reading chapter 4 of professional javascript web developers. on p. 86

primitive values can’t have properties added them though attempting won’t cause error. here’s example:

var name = “nicholas”; name.age = 27; alert(name.age); //undefined

they javascript not treat strings objects, other languages do. wanted see if print out name.age.

i tried

var name = "nicholas"; name.age = 27, alert(name.age);

and got undefined.

trying

var name = "nicholas"; name.age = 27 & alert(name.age);

also gave undefined.

but,

var name = "nicholas"; alert(name.age = 27);

gives 27!

with regards text's original example, author says

"here property called age defined on string name , assigned value of 27. on next line, however, property gone. reference values can have properties defined dynamically later use."

what going on comma separated assignment , function phone call - knew utilize commas separate variable assignments, can function calls? limits comma in javascript? how & operator work chaining code snippets? operator , should used for? why did lastly illustration work when other ones wouldn't? have scope?

edit: jlrishe , sirreal. didn't understand jlrishe's reply until reading sirreal's, recommend reading both!

really, reply 3 of questions has how ,, & , = operators defined, , has nil properties on primitive values.

your sec illustration example of comma operator, , different comma used in variable declarations. evaluates each of operands 1 @ time left right, , ultimate value of look value of lastly operand.

the & operator evaluates 2 operands left right , produces result of applying bitwise and them. alert() executing side effect of this. look 27 & alert(name.age) evaluates 0, , assigned name.age (but doesn't anything). can see similar behavior with:

name.age = 27 * alert(name.age);

or

name.age = 27 - alert(name.age);

or several other operators.

what observed in lastly illustration well-defined behavior of = operator. performs assignment , produces value of right-hand side. assignment doesn't happen in case, reasons quoted, evaluates value of right-hand nonetheless, , passed alert() function.

javascript