{"id":6591,"date":"2022-09-04T04:56:03","date_gmt":"2022-09-03T23:26:03","guid":{"rendered":"https:\/\/jassweb.com\/solved\/solved-difference-between-typeof-andrei-and-typeof-andrei-valueof\/"},"modified":"2022-09-04T04:56:03","modified_gmt":"2022-09-03T23:26:03","slug":"solved-difference-between-typeof-andrei-and-typeof-andrei-valueof","status":"publish","type":"post","link":"https:\/\/jassweb.com\/solved\/solved-difference-between-typeof-andrei-and-typeof-andrei-valueof\/","title":{"rendered":"[Solved] difference between typeof “andrei” and typeof “andrei”.valueOf()"},"content":{"rendered":"

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\n<\/p>\n

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<\/div>\n
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No, there’s no difference, unless someone’s done something silly to the JavaScript environment.<\/p>\n

\"andrei\"<\/code> is a string primitive, thus typeof \"andrei\"<\/code> is \"string\"<\/code>. If you do \"andrei\".valueOf()<\/code>, you’re coercing a string primitive into a String<\/code> object (in theory*) because you’re accessing a property on it (valueOf<\/code>), and then asking that object for its primitive value\u00a0\u2014 which is a primitive string, thus typeof \"andrei\".valueOf()<\/code> is \"string\"<\/code>.<\/p>\n

Of course, you could replace String.prototype.valueOf<\/code> with something other than the default which broke tne String.prototype.valueOf<\/code> contract by returning, say, a number or object. But that’s out in bizarre-land.<\/p>\n

\n

* “in theory” – JavaScript engines are free to optimize operations provided the optimization doesn’t make things behave in a way that isn’t according to spec. So a JavaScript engine could optimize away calling .valueOf()<\/code> on a string primitive provided String.prototype.valueOf<\/code> is still the same as its default value (which the engine can easily be aware of), since the result is just the same as the primitive. I don’t know whether they do<\/em>, but they could.<\/p>\n

\n

Re your comment on the question:<\/p>\n

\n
 if((typeof name !=\"undefined\") && (typeof name.valueOf()==\"string\") && (name.length>0))\n<\/code><\/pre>\n
in this one i deleted valueOf()<\/code> and the result was the same and i was courious about that.<\/p>\n<\/blockquote>\n
Ah! That’s a different thing, for two reasons:<\/p>\n
    \n
  1. \n
    name<\/code> may not be a string. Lots of things have length<\/code> properties\u00a0\u2014 strings, functions, basic arrays, typed arrays, DOM collections, any number of script-defined objects…<\/p>\n<\/li>\n
  2. \n
    name<\/code> may be a String<\/code> object<\/em> (although it’s unlikely, people don’t normally use String<\/code> objects unless writing extension methods for String.prototype<\/code>, in which case this<\/code> refers to a String<\/code> object).<\/p>\n<\/li>\n<\/ol>\n
    So removing that typeof name.valueOf()==\"string\"<\/code> part would change the condition. Re the .valueOf()<\/code> part: The author of that code is either a bit paranoid or there’s a reason to expect that name<\/code> may be a String<\/code> object (and so its type would be \"object\"<\/code>, not \"string\"<\/code>). Using valueOf<\/code> ensures that he\/she is checking the primitive instead.<\/p>\n
    Surprisingly, they weren’t paranoid enough (at least, without context), since null<\/code> would cause an exception in that code.<\/p>\n
    The ()<\/code> around each condition are also completely unnecessary.<\/p>\n
    Handling null<\/code> as well looks like this:<\/p>\n
    if (name != null && typeof name.valueOf() == \"string\" && name.length > 0)\n<\/code><\/pre>\n<\/p><\/div>\n
    <\/div>\n<\/div>\n
                5<\/span> <\/p><\/div>\n<\/div>\n
    [ad_2]<\/p>\n
    solved difference between typeof “andrei” and typeof “andrei”.valueOf() <\/p>\n","protected":false},"excerpt":{"rendered":"
    [ad_1] No, there’s no difference, unless someone’s done something silly to the JavaScript environment. “andrei” is a string primitive, thus typeof “andrei” is “string”. If you do “andrei”.valueOf(), you’re coercing a string primitive into a String object (in theory*) because you’re accessing a property on it (valueOf), and then asking that object for its primitive … Read more<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[320],"tags":[333,362],"class_list":["post-6591","post","type-post","status-publish","format-standard","hentry","category-solved","tag-javascript","tag-string"],"yoast_head":"\n[Solved] difference between typeof "andrei" and typeof "andrei".valueOf() - JassWeb<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/jassweb.com\/solved\/solved-difference-between-typeof-andrei-and-typeof-andrei-valueof\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"[Solved] difference between typeof "andrei" and typeof "andrei".valueOf() - JassWeb\" \/>\n<meta property=\"og:description\" content=\"[ad_1] No, there’s no difference, unless someone’s done something silly to the JavaScript environment. "andrei" is a string primitive, thus typeof "andrei" is "string". If you do "andrei".valueOf(), you’re coercing a string primitive into a String object (in theory*) because you’re accessing a property on it (valueOf), and then asking that object for its primitive ... 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