Your cryptic part isn’t all that cryptic if you rewrite it a little: [][”] [] will be coerced into a string because it isn’t an integer, so you’re looking for a property of [] with the name ” (an empty string). You’ll just get undefined, as there is no property with that name. As for … Read more
In ES5, you can get a reference to global object from within strict mode via indirect eval call: “use strict”; var global = (1,eval)(‘this’); Take a look at my article; particularly at this section on strict mode.
It appears to be O(n) in V8 (chrome, node.js) at least: > var hash = {} > , c = 0; > > var s = +new Date();Object.keys(hash);console.log(+new Date() – s); 0 > for(var i=0; i<100000; i++, c++){ hash[c] = 1; } > var s = +new Date();Object.keys(hash);console.log(+new Date() – s); 26 > for(var i=0; … Read more
Where does the specification say that values of the Object type behave differently than primitives? Is it only that primitives are immutable, and objects are mutable? Yes, it bascially boils down to the mutability of objects, and the identity of objects. Actually, this is not even specified anywhere, it is just assumed as a given … Read more
UPDATE from 2021 Despite this being the accepted answer, 10 years of experience has taught me this isn’t the best idea. Pretty much anything you can do avoid polluting the global scope is a very very good thing. Original answer below, for posterity, and because stack overflow will not let me delete an accepted answer. … Read more
Yes, catch clauses indeed have their own Lexical Environments. Check out what happens when it is evaluated: It creates a new one (deriving from the current one) and binds the exception-identifier to it. When executing the catch block, the current Execution Context’s LexicalEnvironment is switched to the new one, while the VariableEnvironment(“whose environment record holds … Read more
I’ll give this a try. Note that I’m not affiliated with ECMA and have no visibility into their decision-making process, so I cannot definitively say why they have or have not done anything. However, I’ll state my assumptions and take my best shot. 1. Why add a for…of construct in the first place? JavaScript already … Read more
The difference between let and const is that once you bind a value/object to a variable using const, you can’t reassign to that variable. In other words Example: const something = {}; something = 10; // Error. let somethingElse = {}; somethingElse = 1000; // This is fine. The question details claim that this is … Read more
This is all explained very nicely in “Proposed ECMAScript 3.1 Static Object Functions: Use Cases and Rationale” document (pdf) by Allen Wirfs-Brock himself (editor of ES5 spec, and a member of TC39). I would suggest to read all of it. It’s pretty short, easily digestible, and gives a nice glimpse of the thought process behind … Read more
The javascript interpreter/compiler is so smart to only insert automatic semicolons if afterwards there is valid Javascript. Your code works, because && b as it stands is no valid expression – that’s why no semicolon gets inserted after the return a resulting in: return a && b && c; However: return (undefined);//implicitely inserted { …. … Read more