<br><br><div class="gmail_quote">On Sat, Dec 31, 2011 at 7:53 PM, Axel Rauschmayer <span dir="ltr"><<a href="mailto:axel@rauschma.de">axel@rauschma.de</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div style="word-wrap:break-word"><div><div class="im"><blockquote type="cite"><div>1. We want sane isObject and isNull predicates, ideally using typeof. Lack of them continues to bite people, as the web contains code that wrongly assumes typeof x == "object" => x.foo won't throw on null x.<br>
</div></blockquote><div><br></div></div><div>What are the use cases for typeof? Offhand, I see five and for most of them, other solutions seem to be better.</div></div></div></blockquote><div><br></div><div><div>In my experience the major use of typeof is to implement dynamic function overloading.  That is, a function that is flexible in the arguments it takes, such that one logical name maps to multiple use cases.</div>
</div><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div style="word-wrap:break-word"><div><div><br></div><div>1. Checking whether a variable has been declared.</div>
<div>    Problematic: verbose and conflated with checking for a declared variable having the value `undefined`.</div><div>    Better: a dedicated operator or predicate for performing this check.</div></div></div></blockquote>
<div><br></div><div>Sorry, I don't think anyone checks if a is variable declared. You just look at the source code.</div><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div style="word-wrap:break-word"><div><div><br></div><div>2. Checking that a value is neither null nor undefined.</div><div>    Problematic: can’t be done via only typeof currently.</div><div>    Better: a predicate for performing this check. This use case will become less important with default parameter values.</div>
</div></div></blockquote><div><br></div><div>if(!name) {}</div><div><br></div><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div style="word-wrap:break-word">
<div><div><br></div><div>3. Distinguishing between objects and primitives.</div><div>    Problematic: Made more difficult by typeof null === "object" and typeof function () {} === "function".</div><div>
    Better: predicates such as isObject() and isPrimitive()</div></div></div></blockquote><div><br></div><div>Mostly we are checking string, array, function or object.  Only Java devs pass/return |null| so that case is not that big of a deal. Or another way to look at it: if you use null, it's your own little signal, so enjoy.</div>
<div><br></div><div>Array is the famously difficult case.</div><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div style="word-wrap:break-word"><div><div>
<br></div><div>4. Determining the type of a primitive value.</div><div>    Better: typeof is OK here, but changing it so that typeof null === "null" would help.</div><div><br></div><div>5. Determining the type of a value (primitive or otherwise).</div>
<div>    Better: I would want a function, e.g. getTypeName() that works like (null-enabled) typeof for primitives and returns the value of the [[Class]] property for objects.</div></div></div></blockquote><div><br></div><div>
This would be great!</div><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div style="word-wrap:break-word"><div><div><br></div><div>Everything except #1 can be easily implemented as functions (and be brought to ES5 via shims). A function such the #5 getTypeName() could take care of use case #4, as well.</div>
<div><br></div><div>Ideas for getTypeName(): <a href="http://www.2ality.com/2011/11/improving-typeof.html" target="_blank">http://www.2ality.com/2011/11/improving-typeof.html</a></div><div><br></div></div><div class="im">
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<div style="margin-top:0px;margin-right:0px;margin-bottom:0px;margin-left:0px"><span style="font-size:medium"><div style="margin-top:0px;margin-right:0px;margin-bottom:0px;margin-left:0px">-- </div><div style="margin-top:0px;margin-right:0px;margin-bottom:0px;margin-left:0px">
Dr. Axel Rauschmayer</div><div style="margin-top:0px;margin-right:0px;margin-bottom:0px;margin-left:0px"><a href="mailto:axel@rauschma.de" target="_blank">axel@rauschma.de</a></div><div style="margin-top:0px;margin-right:0px;margin-bottom:0px;margin-left:0px">
<br></div><div style="margin-top:0px;margin-right:0px;margin-bottom:0px;margin-left:0px"><div style="margin-top:0px;margin-right:0px;margin-bottom:0px;margin-left:0px">home: <a href="http://rauschma.de" target="_blank">rauschma.de</a></div>
twitter: <a href="http://twitter.com/rauschma" target="_blank">twitter.com/rauschma</a></div><div style="margin-top:0px;margin-right:0px;margin-bottom:0px;margin-left:0px">blog: <a href="http://2ality.com" target="_blank">2ality.com</a></div>
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