Optimization improvement in jQuery.extend

[anonymous]

On line 313 of core.js:

​https://github.com/jquery/jquery/blob/master/src/core.js#L313

there is a check for:

typeof target === "boolean"

However, target has been set by:

target = arguments[0] || {},

so in case it's a boolean, it's always true (if arguments[0] was false, target is {}). Checking for true is much faster than a typeof check and then comparing strings, especially on IE:

​http://jsperf.com/true-vs-typeof

Thanks for considering this optimization.

[timmywil]

Seems to me that this will not set the target correctly if both false and a target is passed to extend. That may not happen very often, but would be a regression.

$.extend( false, { some: "target" }, { more: "stuff" } );

[dmethvin]

More often than I would have expected, that's fer sure.

​http://google.com/codesearch#search/&q=\$\.extend\(\s*false

There are probably more of the form $.extend(iCanHazDeep, defaults, options) but they're too hard to grep.

[rwaldron]

If arguments[0] is any kind of falsy, it's not boolean by the time it reaches that condition.

[rwaldron]

Sorry, by "it" I meant the target var

[rwaldron]

Turns out this is a performance hit, so no thanks.

[timmywil]

This is now neither here nor there, but let me explain further. I don't think this would work anyway because target needs to get assigned to arguments[1] even if arguments[0] is false. It can't just be an empty plain object. The only place that happens is from within the typeof conditional, so it can't change unless that assignment is added somewhere else and at that point we're talking about changing more than just the conditional.

[rwaldron]

#10867 is a duplicate of this ticket.