Things in JS are passed (to functions) by value, because direct assignment to the binding isn't visible outside the function (take no note of sloppy-mode `arguments` over there behind the curtain. ES Module live-bindings of exports add a wrinkle, as well)
I've found https://web.archive.org/web/20161005155047/http://www.jon-carlos.com/2013/is-javascript-call-by-value-or-call-by-reference/ helpful. On Sat, Aug 26, 2017 at 1:26 PM, Michael Dyck <[email protected]> wrote: > On 2017-08-26 05:40 AM, Danny Niu wrote: > >> Hi all, I've been struggling finding information on this, so let me open >> by asking the following question: >> >> Q1: If primitive types are passed by value and objects by reference when >> calling function, where is this characteristic of objects mentioned in >> the standard? >> > > Objects aren't "passed by reference" according to the original/usual sense > of that term. > > People from https://stackoverflow.com/questions/518000 seems adamant that >> ES is a pass-by-value language, so I assumed the value of objects are >> their individuality. >> > > The top two answers there both say (more or less) it's pass-by-value, and > for objects, the 'value' is a reference to the object. > > So you might wonder why objects are special in this regard. But they > aren't: > if you like, you can imagine everything being passed by value, where the > 'value' is a reference to the thing. > > Q2: What's the rationale if any, to not explicitly require that objects >> be viewed as reference when passed as arguments to functions and assigned >> to variables. >> > > One reason might be to avoid confusion with the Reference type. Another > reason might be to avoid making a distinction that the spec will never (or > rarely) use. > > When you pass a value to a function-parameter or assign a value to a > variable, you are (in spec terms, more or less) binding that value to an > identifier name, i.e., creating an association between the name and the > value. > > Given that terminology, I don't think it helps to add "reference" to the > description. It's enough to understand that a value can participate in > multiple bindings/associations at the same time. But you're free to imagine > references being involved in the implementation. > > -Michael > > _______________________________________________ > es-discuss mailing list > [email protected] > https://mail.mozilla.org/listinfo/es-discuss >
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