Comments on: Guarding in JavaScript

By: Emmett

Emmett — Sun, 04 May 2008 17:25:52 +0000

width = specs && specs.width;
is not exactly the same thing as
if(specs.width) width = specs.width;
The first will always overwrite the value of width; the second will only overwrite width if specs.width exists.

By: h3

h3 — Sun, 04 May 2008 07:36:19 +0000

Yeah it’s one of the many things I like in JavaScript (http://www.haineault.com/blog/44/).

It’s also useful to combine it with the “||” operator, like this:

width = specs && specs.width || default.width;

By: kushal

kushal — Sun, 04 May 2008 00:56:01 +0000

C# has an equivalent of || too. As does SQL: http://kushalm.com/the-null-coalescing-operator-or-how-to-make-default-values-sound-frightening

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Sat, 03 May 2008 15:30:50 +0000

[...] [JAVASCRIPT] Guarding in JavaScript, thoughtworker.in, via:lazycoder.com [...]

By: engtech

engtech — Fri, 25 Apr 2008 16:11:24 +0000

Check out Reg’s andand gem for ruby as well.

It lets you do the equivalent of && in method chains.

http://andand.rubyforge.org/

By: prakash

prakash — Fri, 25 Apr 2008 13:23:55 +0000

Another important aspect of these operators is the “short-circuiting” behavior. The second operand is evaluated only if the first operand can not determine the value of the expression. In the case of ‘||’ operator, for example, the second operand isn’t evaluated if the first operand is true.

Most dynamic languages whose ancestry can be traced back to C (which was the first to “spell” these operators like this) support this type of logical operator behaviour.

AFAIK, Perl was the the first language that borrowed this “short-circuit” behavior from C and and improved it. Whereas in C the expression in the RHS evaluates to either 0 or 1, in most dynamic languages, the RHS evaluates to one of the two operands. This improvement, as you have noticed, gives rise to very concise and efficient, yet readable, code.

By: Sid

Sid — Fri, 25 Apr 2008 04:33:50 +0000

Ruby does the same thing with both && and ||