Is this lazy variable initialization pattern bad practice?

Question

Coming from the rubyesque crowd I was very fond of the following 'lazy' initialization pattern.

myhash[:property]||='value'

And sometimes during my career I adapted it to javascript as following:

myhash.property || (myhash.property = 'value')

A co-worker remarked that it's quite irregular, and to be honest I can't remember seeing other people using that pattern.

So my question is; Is it just another innocent initialization flavor or am I unintentionally asking for trouble?

Given the execution flow of conditional statements like that I suppose It is possible to use it as an if statement aswell:

aModel.valid && aModel.save();

or even something more insane..

willYouMarryMe === 'yes' && (function(){
  console.log('Wohoo!');
})();

Remember that JavaScript has many more false-y values than Ruby: sometimes you want a 0 to stay a 0. As far as code style, I avoid strict side-effects in conditionals, as I find it harder to understand. — user2864740
– user2864740, Commented Jan 2, 2014 at 2:58

Community · Accepted Answer · 2020-06-20 09:12:55Z

10

Lazy initialization is often used in JavaScript, but it's more common to see:

namespace.property = namespace.property || 'default';

As far as calling functions is concerned, it's good practice to use if statements where they apply instead of && and ||. Minifiers will often automatically convert the if statements into && and || for production to reduce file size, so it's not necessary to do so directly.

Writing easily readable code makes future maintenance easier:

_Good:

if (!foo) {
    bar();
}

Writing code that's harder to read makes code harder to maintain. Particularly because using one clever trick often indicates that other clever tricks are going to be used:

_Bad:

foo || bar();

The one major exception to this with regard to functions tends to be when calling console.log:

window.console&&console.log('lorem', 'ipsum');

edited Jun 20, 2020 at 9:12

CommunityBot

11 silver badge

answered Jan 2, 2014 at 2:57

zzzzBov

180k57 gold badges328 silver badges375 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

telamon Over a year ago

Thanks, that pretty much answers my question. My followup question would be, is it safe to expect that expression evaluation behaves the same across different js-engines? Somewhere i get the feeling that there might not be an explicit prohibition to evaluate the right-hand expression if the former expression is false in the ECMA standard. ( Gee.. I probably should go dig there for further info )

zzzzBov Over a year ago

@telamon, it sounds like you're asking whether the short-circuit evaluation behavior of the && and || operators is part of JavaScript as a language, or whether it's just part of some implementations. If I've interpreted your question correctly the answer is that it's a defined behavior as part of the ECMAScript standard (&& and || will not evaluate the second argument unless the first argument is truthy or falsey respectively). If I've misunderstood your question, please elaborate.

telamon Over a year ago

Thanks, you nailed it! In retrospect that was exactly the question I've been searching for.

Collectives™ on Stack Overflow

Is this lazy variable initialization pattern bad practice?

1 Answer 1

3 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

3 Comments

Your Answer

Sign up or log in

Post as a guest

Related