Are you putting hundreds of classes into a single scope? On Tue, Dec 8, 2015 at 11:56 PM, John Gardner <[email protected]> wrote:
> Trouble is, if one has literally hundreds of classes or functions that > need to be matched, they'd rather not pool them all into one massive object > literal for the sake of easier mapping. DRY principle fully relevant. > > Also, yes, while it would be a pain for static type analysis, it wouldn't > necessarily be the same as `eval`. Eval executes arbitrary code, whereas > the indirect references would only point to modifiers only: > > var className = \"doSomethingSinister(/etc/passwd/);" > > That line would literally be looking for a property in the current scope > that'd be named this: > > global["doSomethingSinister(/etc/passwd/);"] > window["doSomethingSinister(/etc/passwd/);"] > > > > On 9 December 2015 at 16:09, Frankie Bagnardi <[email protected]> > wrote: > >> This is a common situation, but one easily solved by object literals. >> Reflecting on the scope is confusing and would hurt tooling (it's >> essentially eval). >> >> ```js >> var mapping = {Polygon: Polygon}; >> var meshClass = mapping[ajaxData.className]; >> ``` >> >> >> >> >> On Tue, Dec 8, 2015 at 9:53 PM, John Gardner <[email protected]> >> wrote: >> >>> ECMAScript currently offers no clean way to "dereference" a variable in >>> the current scope. For instance, assume an author wishes to obtain a >>> reference to a class using a variable that holds its name: >>> >>> class Paintbrush{ } >>> >>> let className = "Paintbrush"; >>> >>> // Would only work in browsers, not NodeJS >>> console.log( window[className] ); >>> >>> // Doesn't even work in NodeJS >>> console.log( global[className] || this[className] ); >>> >>> A hacky workaround is to create an anonymous function that simply >>> returns a reference to the named variable: >>> >>> function dereference(name){ >>> return new Function([], "return " + name)(); >>> } >>> dereference("Paintbrush") === Paintbrush; // true >>> >>> This isn't an elegant solution, nor a preferable one. Another approach >>> might be to leverage `eval`, which opens up the obvious issues of >>> performance and security. >>> >>> Having a way of indirectly referencing another variable would fix this: >>> >>> class Paintbrush{ } >>> >>> let className = "Paintbrush"; >>> >>> let classReference = \className; >>> console.log(classReference === Paintbrush); // true >>> >>> Sticking a backslash before a bareword identifier creates a reference to >>> an object whose name matches the identifier's string value. If no such >>> object exists in the current scope, it simply returns `undefined`. >>> >>> I can't see this being used in everyday programs, but it would >>> facilitate Ajax programming considerably, where classes or functions can >>> only be specified by name: >>> >>> {"className":"Polygon", "vertices": [[0,0]...] } >>> >>> let meshClass = \ajaxData.className; >>> if(meshClass instanceof Mesh){ >>> new meshClass(ajaxData.vertices); >>> } >>> >>> >>> >>> >>> _______________________________________________ >>> es-discuss mailing list >>> [email protected] >>> https://mail.mozilla.org/listinfo/es-discuss >>> >>> >> > > _______________________________________________ > es-discuss mailing list > [email protected] > https://mail.mozilla.org/listinfo/es-discuss > >
_______________________________________________ es-discuss mailing list [email protected] https://mail.mozilla.org/listinfo/es-discuss
