PHP：做这个|| 那（就像javascript）

In javascript we can use || to perform a second action if the first one fails, like:

function getObject(id_or_object) {
    var obj = document.getElementById(id_or_object) || id_or_object;
    return obj;
}

How can we do this in PHP?

If we can't, I can swear I have seen this || used like this in PHP. What does it mean?

I want to do:

function fix_item($item) {
    $item['armor'] = $item['armor'] || 0;
    return $item;
}

But this doesn't work, so I'm using

function fix_item($item) {
    if (!isset($item['armor'])) $item['armor'] = 0;
    return $item;
}

, but I don't like the second method.. Any ideas?

You can use || (OR) for true/false comparison, but (this is one of the known (arguable) design errors) in PHP's design: short-circuit doesn't return the operand's value (as you were doing in your javascript-logic example) but the boolean result.

That means that:
$item['armor'] = $item['armor'] || 0; does not work as you intended (like it would in javascript).
Instead, it would set $item['armor'] to boolean true/false (depending on the outcome of: $item['armor'] || 0 ).

However, one can use the 'lazy evaluation' in a similar manner as you can use it in javascript:
isset($item['armor']) || $item['armor'] = 0;
(with an added isset to prevent an Undefined variable error).
It still clearly describes what your intention is and you don't need to invert the boolean isset result using ! (which would be nececary for if and && (AND)).

Alternatively, one can also do:
$item['armor'] = $item['armor'] OR $item['armor'] = 0; (note that this will give an E_NOTICE)
(I think readability is not so good),

or ternary:
$item['armor'] = isset($item['armor']) ? $item['armor'] : 0;
(with 'better'/'more common' readabilty, but added code-size).

For PHP7 and up, see Tom DDD 's answer.

if you are using php 7 you can use the null coalesce operator

$a ?? $b ?? $c 

this evaluates to the first non null value. Which is very simmilar to the || from javascript.

This tests $item['armor'], if it is true it returns what is to the right of the ? operator, if it is false it returns what is immediately to the right of : (I've used the ternary operator in javascript, too).

function fix_item($item) {
    $item['armor'] = $item['armor'] ? $item['armor'] : 0;
    return $item;
}