for-in-loop

问题 I found this answer: https://stackoverflow.com/a/5163334/1364174 Which presents how for in loop is implemented. NSFastEnumerationState __enumState = {0}; id __objects[MAX_STACKBUFF_SIZE]; NSUInteger __count; while ((__count = [myArray countByEnumeratingWithState:&__enumState objects:__objects count:MAX_STACKBUFF_SIZE]) > 0) { for (NSUInteger i = 0; i < __count; i++) { id obj = __objects[i]; [obj doSomething]; } } The problem is that, I found it wrong. First of all, when you have Automatic

问题 I'm working on a JS to show different messages depending on the current url's hash. Now, that's all working, but I was wondering what the best way would be to access my messages (They'll be coded into a .js file) At the moment, I have the messages stored in a object like this: popups = { TemplateMessage: { title: "Template Popup Title", message: "This is a template popup message! Copy this to add a message.", modal: true }, AnotherMessage: { title: "another title", message: "message.", modal:

问题 What is the difference between for..in and for each..in statements in javascript? Are there subtle difference that I don't know of or is it the same and every browser has a different name for it? 回答1: "for each...in" iterates a specified variable over all values of the specified object's properties. Example: var sum = 0; var obj = {prop1: 5, prop2: 13, prop3: 8}; for each (var item in obj) { sum += item; } print(sum); // prints "26", which is 5+13+8 Source "for...in" iterates a specified

问题 What's the correct way to write a for-in loop in JavaScript? The browser doesn't issue a complaint about either of the two approaches I show here. First, there is this approach where the iteration variable x is explicitly declared: for (var x in set) { ... } And alternatively this approach which reads more naturally but doesn't seem correct to me: for (x in set) { ... } 回答1: Use var , it reduces the scope of the variable otherwise the variable looks up to the nearest closure searching for a

问题 So, I'm still reading Apress Pro Javascript Techniques and i'm having troubles with closures. As John Resig states: Closures allow you to reference variables that exist within the parent function. However it does not provide the value of the variable at the time it is created; It provides the last value of the variable withing the parent function. The most common issue under which you'll see this occurr during a for loop. There is one variable being used as an interaor (e.g., i). Inside of

问题 This question already has answers here : How can I replace one class with another on all elements, using just the DOM? (2 answers) Closed 4 years ago . I have a page (actually, about thirty or so) where I'm trying to change the classname of specific elements based on a querystring variable. Everything works fine except for this part, I'm getting a really weird result... var hitAreas = document.getElementsByClassName('hitArea'); alert(hitAreas.length); for(hitArea in hitAreas) { alert(hitAreas

问题 This question already has answers here : ECMAScript 2015: const in for loops (3 answers) Closed 2 years ago . Why JavaScript const works same as let in for in loop? const is using to declare constants in EC6. Then why the const num value getting updated in each iteration of the for in ? For in with let for (let num in nums) { console.log(num); // works well, as usual } For in with const for (const num in nums) { console.log(num); // why const value getting replaced } 回答1: Why JavaScript const

问题 So I'm a JS newbie and am trying to figure out how to fix my problem. I am trying to loop over an object and return the lowest number. in my var shortest = ; if I hardcode a number say var shortest = 455; then the problem returns the correct number 3. although im not sure what to put there to make it blank by default. I have tried object[0] , object[key] and '' and none of these work properly var myObj = {first: 45, second: 23, third: 3, fourth: 222, fifth: 2343}; var myFunc = function

问题 This question already has answers here : Closed 8 years ago . Possible Duplicate: JavaScript “For …in” with Arrays I'm trying to use the for-in syntax to loop through an array of numbers. Problem is, those numbers are getting converted to strings. for(var element in [0]) { document.write(typeof(element)); // outputs "string" } Is this standard behavior? I can think of a bunch of ways to work around it, but I'm really just looking for an explaination, to expand my understanding of JavaScript.

问题 I'm storing 5 PFFiles in an array and using getDataInBackgroundWithBlock to download those files from Parse. The problem is the order at which they appear in the table view cells is different every time, presumably because the files are download at different speeds due to the different file sizes. for (PFFile *imageFile in self.imageFiles) { [imageFile getDataInBackgroundWithBlock:^(NSData *imageData, NSError *error) { if (!error) { UIImage *avatar = [UIImage imageWithData:imageData]; [self