Reputation: 15
I am in need of understanding the below java script code, written by someone else. Can you please tell me what the below line means (particularly fourth line).? It is a single lengthy line (till ;). It is not a puzzle. It is a shopping application's code, practically in use (not altered).
function trackMetrics(a,b,c,d)
{
var e=a,f=b,g=c,h=d;
typeof a=="object"&&(a.type!=null&&(e=a.type),a.action!=null&&(e=a.action),a.data!=null&&f=a.data),a.map!=null&&(g=a.map),a.load!=null&&(g=a.load)),typeof f=="object"&&(f.data!=null&&(f=f.data),f.map!=null&&(g=f.map),f.load!=null&&(h=f.load)),typeof g=="object"&&(g.map!=null&&(g=g.map),g.load!=null&&(h=g.load));
Upvotes: 1
Views: 255
Reputation: 22727
Just break it into pieces, understanding each by itself, then you can put together the meaning of the whole.
Note that the && operator will stop processing the following conditions when it reaches a false value (called short-circuiting). The comma operator will cause each of the expressions they separate to be executed regardless of the results. Together, they are used by this code to do a lot of logical testing and assignments in one line. (And it is definitely ok to say, "Yuck!" here.)
typeof a=="object" // If a is of type "object"
&& ( // then
a.type!=null // if a.type != null
&&(e=a.type) // then e = a.type
,a.action!=null // if a.action != null
&&(e=a.action) // then e = a.action
,a.data!=null // ... and so on ...
&&f=a.data)
,a.map!=null
&&(g=a.map)
,a.load!=null
&&(g=a.load)
)
,typeof f=="object"
&&(
f.data!=null
&&(f=f.data)
,f.map!=null
&&(g=f.map)
,f.load!=null
&&(h=f.load)
)
,typeof g=="object"
&&(
g.map!=null
&&(g=g.map)
,g.load!=null
&&(h=g.load)
)
;
After looking it over, it would be tempting to assume that it does nothing, but there are assignments embedded in some of the conditions (like g=a.map
). So, you'll need to process the logic (and hopefully understand the meaning) to see what conditions will cause which values to be set.
Upvotes: 0
Reputation: 123573
Well, currently, it means a SyntaxError
as it has an unmatched )
just before:
typeof f=="object"
But, it appears to be using the comma operator to group multiple statements (vs. ;
) and is using &&
's short-circuiting as an alternative to an if
statement.
if (typeof a == "object") {
if (a.type != null)
e = a.type;
if (a.action != null)
e = a.action;
if (a.data != null)
f = a.data;
}
if (a.map != null)
g = a.map;
// etc.
Upvotes: 2