Comments on: And and Or in JS

By: Theodor Zoulias

Theodor Zoulias — Sat, 24 Sep 2005 23:00:58 +0000

Interesting. I’ve only used Error constructor server-side, with JScript. But is cross-browser supported? It seems that IE5 knows nothing about property “message” and returns undefined. My purpose was just to give an example where OR operator becomes handy. Saves bytes too!

By: Erik Arvidsson

Erik Arvidsson — Sat, 24 Sep 2005 13:14:00 +0000

Theodor: I’m not sure what that was an answer to but those are some interesting code snippets. Here is another one:

try {
throw new Error(”my error”); // new can be omitted
} catch(e) {
alert(e.message)
}

IE: my error
FF: my error
Opera: my error

By: Theodor Zoulias

Theodor Zoulias — Sat, 24 Sep 2005 11:43:23 +0000

try {
a
} catch(e) {
alert(e)
}

IE: [object Error]
FF: ReferenceError: a is not defined
——————————————
try {
throw ‘my error’
} catch(e) {
alert(e.message)
}

IE: undefined
FF: undefined
——————————————
try {
a
} catch(e) {
alert(e.description || e.message || e)
}

IE: ‘a’ is undefined
FF: a in not defined

By: Erik Arvidsson

Erik Arvidsson — Fri, 09 Sep 2005 23:45:39 +0000

I don’t think you need to care about the performance here. The || operator should be slightly faster but compared to the slow DOM code browsers have it is just a drop in the ocean.

The expressions are not identical because that would break semantics. When using the ternary operator the expression is executed twice. Here is a test case that shows that they are different:

var c = 0;
function f() {
return c++;
}

var a = f() || ‘a’; // ‘a’
var b = f() || ‘b’; // 1

// reset
c = 0;

a = f() ? f() : ‘a’; // ‘a’
b = f() ? f() : ‘b’; // 2

By: Alberto

Alberto — Fri, 09 Sep 2005 23:26:14 +0000

var el = e.target || e.srcElement;

Ternary still looks clearer. Yet this one has always had its appeal.
The only thing I always wondered about these approaches is: has anyone found a reliable way to benchamrk the both of them and see what type of performance gain there can be- if any?
That is, without having to wait 2 hours (which no js interpreter would allow) before having a meaningful difference.

By: Patrick Corcoran

Patrick Corcoran — Tue, 30 Aug 2005 19:34:16 +0000

I did some basic performance tests iterating over 1,000,000 iterations of each syntax, and no performance difference between the two syntaxes was noticeable.

I would guess from this that they are identical after “compilation”.

By: Jeremy

Jeremy — Wed, 13 Jul 2005 18:56:36 +0000

And I can’t even type my own effin’ name. hahaha

By: Jerem

Jerem — Wed, 13 Jul 2005 18:55:40 +0000

It usually gets me in trouble (or I’m told it’s not proper)… but if it saves me lines, I run with it. I have a line like this in one of my scripts:

this.node = oNode || false;
this.value = sValue || (this.node && this.node.text) || false;

I don’t have a problem reading it, but that’s just me.

By: Erik Arvidsson

Erik Arvidsson — Tue, 12 Jul 2005 09:35:21 +0000

Well, you usually use || if one of the alternative objects are avaialable. Ternary expression are useful but for different reasons. I agree that nesting ?: is usually a bad idea.

By: Robert Nyman

Robert Nyman — Tue, 12 Jul 2005 09:26:54 +0000

When it comes to ternary expressions, I agree. Depends on how complex it is.
The example in your post is ok, I think, but when you have more options it’s not the best way to go.

For example, this is not desirable for me, if...else would be better in this case:

var el = (e.target)? (bIsTuesday)? e.target : e.keyCode : e.srcElement;