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问题 I have noticed that there doesn't appear to be a clear explanation of what the this keyword is and how it is correctly (and incorrectly) used in JavaScript on the Stack Overflow site. I have witnessed some very strange behaviour with it and have failed to understand why it has occurred. How does this work and when should it be used? 回答1: I recommend reading Mike West's article Scope in JavaScript (mirror) first. It is an excellent, friendly introduction to the concepts of this and scope

问题 Closed . This question needs details or clarity. It is not currently accepting answers. Want to improve this question? Add details and clarify the problem by editing this post. Closed 6 years ago . Anyone have any idea why this code gives the error ? "Fatal error: Using $this when not in object context" This is part of a script that I am trying to get working. Thanks function add($is_general_media, $title, $description, $allowed_extensions, $display) { $db = new db; if (User::isAdmin()) {

问题 I'm attempting to grab the characters after an index to use in selecting another input with the same last character(s). Currently I have the following error message : thisObj1.indexOf is not a function for thisObj and thisObj1 . I've tried to use a for loop and i with selector, however that resulted in all elements similar being affected. <input type="text" value="5" id="nosday"><br><br> <input type="hidden" value="3" id="countrows"><br> ////////////////////////FIRST FORM/////////////////////

问题 I have a little question. $('.item').mouseenter(function() { setTimeout(function() { $(this).find('.item-overlay').css('z-index', '-1'); }, 300); }).mouseleave(function() { $(this).find('.item-overlay').css('z-index', ''); }); <div class="item"> <div class="item-overlay"> </div> <iframe>...</iframe> </div> Everything works fine, except one small thing. z-index isn't changing. Can you guys help me out with this? I've also tried with "next", "child", "find" - none worked :( 回答1: this within the

问题 Suppose I have the following class: * .h : class MyClass{ void caller(); int threadProcuder(void *args); }; * cpp : void MyClass::caller() { pthread_t i; pthread_create(&i,NULL,(void*(*)(void*))&MyClass::threadProcedure,(void*)this); } int MyClass::threadProcedure(void *args) { cout << "body of thread" << endl; } Unforunately, thread doesn't run. 回答1: The correct way is: // Must declare the callback is extern "C" // As you are calling back from a C library. // As this is compiles as C it can

问题 I would use a small code to explain my question: class C { int a; public: func() { a = 4; }; }; int main() { C obj1; obj1.func(); return 0; } Here func() method tries to set a (a data member of obj1 ) to a value of 4. How does func() get access to a ? Is it because func() has access to this* for obj1 ? If that's true, how does func() get access to this* ? Is it passed to func() as an implicit argument while calling obj1.func() from main() ? If it's passed as an argument, does main() stack

问题 I'm getting an error that I think is because I've made some kind of mistake in a refactoring, but I can't find documentation on when $this is bound, and my error could be explained by it being bound statically. Extra points (I can't actually give you extra points) for links to excellent documentation about this kind of thing in php. [Edit] The error that I'm getting is telling me that Subclass::$var doesn't exist when I do, for example, echo $this->var in a superclass. The $var exists in the

问题 I have a typescript app that it is mixing 'this' context inside a class. This class is responsible to setup new Express server instance. If I track 'this' with debugger and node --inspect-brk we can see 'this' is undefined when serverProtocol gets resolved but it does not matter! I've setup a little project to show what i'm facing. $> git clone https://github.com/AdSegura/ThisLoseContext.git $> cd ThisLoseContext/ $> npm i $> npm run build && node dist/ What output should expect: INIT: Server

问题 This question already has answers here : Do let statements create properties on the global object? (5 answers) why don't const and let statements get defined on the window object [duplicate] (2 answers) Closed 5 months ago . I'm trying to better understand the use of this . In experimenting with this code, I found I can access the items in arr by using something like console.log(this.arr[4]) , but only if arr is declared using var . If I declare arr using let or const , I get a TypeError.

问题 class LoginForm extends Component { state = { email: '', password: '', alert: 'Please Enter Your Email And Password' } onButtonPress() { const { email, password } = this.state; this.setState({ alert: 'Please Try Again' }); firebase.auth().signInWithEmailAndPassword(email, password) .catch(() => { firebase.auth().createUserWithEmailAndPassword(email, password) .catch(() => { this.setState({ alert: 'Login/Registeration Failed.' }); }); }); } render() { return ( <Card> <CardSection> <Button text