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POCan you use .valueOf () to build better ifString function?
 

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  1. POCan you use .valueOf () to build better ifString function?
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    <p>Simplest fool proof(?) method to check for string object I've seen. Tested with many different objects types. Are there parameters/circumstances that might trip it up, and are there simper functions available?</p> <pre><code>function isString(o){ if(o == null || o == undefined){ return false; } if(typeof(o) == 'string'){ return true; } if(typeof(o) == 'object'&amp;&amp; typeof(o.valueOf) == 'function' &amp;&amp; typeof(o.valueOf()) == 'string'){ return true; } return false; } </code></pre> <p>Here's what I've check with:</p> <pre><code>&lt;html&gt; &lt;body&gt; &lt;script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.4/jquery.min.js"&gt;&lt;/script&gt; &lt;input id="el"&gt; &lt;script type="text/javascript"&gt; function isString(o){ if(o == null || o == undefined){ return false; } if(typeof(o) == 'string'){ return true; } if(typeof(o) == 'object'&amp;&amp; typeof(o.valueOf) == 'function' &amp;&amp; typeof(o.valueOf()) == 'string'){ return true; } return false; } function tellIfString(o){ if(isString(o)){ return "A string!&lt;br /&gt;"; }else{ return "Not a string!&lt;br /&gt;"; } } function CustomO(a){ this.a = a; } literal = 'string'; objectWrapped = new String('why do i feel different?'); stringNumber = '345'; number = 234; numberWrapped = new Number(3345); object = {}; array = []; bool = true; nan = 1*'sdf'; regex = /woop/; regex_o = new RegExp('asasd'); o_no_valueOf = {}; o_no_valueOf = delete(o_no_valueOf.valueOf); customO = new CustomO({}); document.write("literal Is "+tellIfString(literal)); document.write("objectWrapped string Is "+tellIfString(objectWrapped)); document.write("stringNumber Is "+tellIfString(stringNumber)); document.write("number Is "+tellIfString(number)); document.write("numberWrapped Is "+tellIfString(numberWrapped)); document.write("object Is "+tellIfString(object)); document.write("array Is "+tellIfString(array)); document.write("bool Is "+tellIfString(bool)); document.write("nan Is "+tellIfString(nan)); document.write("null Is "+tellIfString(null)); //document.write("notdefined Is "+tellIfString(notdefined));//don't need to check variables that haven't been defined, they error before they get to the function document.write("undefined Is "+tellIfString(undefined)); document.write("Math Is "+tellIfString(Math)); document.write("function Is "+tellIfString(function(){})); document.write("regex Is "+tellIfString(regex)); document.write("regexO Is "+tellIfString(regex_o)); document.write("o_no_valueOf Is "+tellIfString(regex_o)); document.write("customO Is "+tellIfString(customO)); document.write("jQuery return Is "+tellIfString($('#el'))); document.write("document Is "+tellIfString(document));//this case is important because it requires the typeof(o.valueOf) == 'function' document.write("window Is "+tellIfString(window)); document.write("document.cookie Is "+tellIfString(document.cookie)); document.write("window.open Is "+tellIfString(window.open)); document.write("window.location Is "+tellIfString(window.location)); document.write("All objects evaluated!"); &lt;/script&gt; &lt;/body&gt; &lt;/html&gt; </code></pre> <p>See also(especially the parts about <code>new String</code> and <code>.valueOf()</code> <a href="https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/String" rel="nofollow">https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/String</a> </p>
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    1. COWhat's your question? This is not a blog. However, this function will incorrectly classify `{valueOf: function() {return 'foo';} }` as string. Better might be: `if(({}).toString.call(o) === '[object String]')`
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      1. USFelix Kling
    2. COIs there a question here, or did you just want to post a function you made?
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    3. COI would recommend reworking this into a question with an answer. We encourage information sharing provided you comply with the guidelines: http://meta.stackexchange.com/questions/17463/can-i-answer-my-own-questions-even-those-where-i-knew-the-answer-before-asking also: http://blog.stackoverflow.com/2011/07/its-ok-to-ask-and-answer-your-own-questions/
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      1. USKev
 

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