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- What is the difference between prototype and prototype chain
- The difference between prototype and prototype chain is: 1. Prototype is an attribute that each object has, including some shared attributes and methods, which is used to realize the sharing and inheritance of attributes and methods between objects, while prototype chain is a The inheritance mechanism is implemented through the prototype relationship between objects, which defines the inheritance relationship between objects so that objects can share the properties and methods of the prototype object; 2. The function of the prototype is to define the shared properties and methods of the object, so that multiple Objects can share the properties and methods of the same prototype object, and the function of the prototype chain is to realize the inheritance relationship between objects, etc.
- Front-end Q&A 876 2023-11-09 16:48:16
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- Why does the front end have implicit type conversion?
- The reasons for implicit type conversion in the front end include weak type features, operator overloading, loose comparison and function parameter passing. Detailed introduction: 1. Weakly typed features. JavaScript is a weakly typed language. The type of a variable is determined by the value assigned, not by the type when declared. This means that the type of the variable can change at runtime. This results in the need for type conversion when performing calculations in expressions; 2. Operator overloading, operators in JavaScript can be applied to different types of operands, etc.
- Front-end Q&A 733 2023-11-09 14:27:50
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- What are the benefits of cast
- The benefits of forced type conversion include extended functions, saving memory space, improving efficiency, interface adaptation, heterogeneous data conversion and code simplification. Detailed introduction: 1. Extended functions. Forced type conversion can make the program have wider functions. By converting a certain data type to another data type, you can use features and operations that are not originally available; 2. Save memory space. Some data types may occupy a large memory space, and the actual data range required may be small by converting a larger data type to a smaller data type, and so on.
- Front-end Q&A 654 2023-11-09 14:21:13
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- What are the risks of casting
- The risks of forced type conversion include data loss, precision issues, memory overflow, runtime errors, logic errors or reduced code readability. Detailed introduction: 1. Data loss. The range of one data type may be smaller than another data type. When converting a data type with a larger range into a data type with a smaller range, data loss may occur; 2 , Precision issues, when performing numerical type conversion, the accuracy may be affected; 3. Memory overflow, when performing forced type conversion, may cause memory overflow problems; 4. Runtime errors, etc.
- Front-end Q&A 1042 2023-11-09 14:16:45
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- What are the characteristics of built-in objects?
- The characteristics of built-in objects include pre-definition, methods and properties, extensibility, typing, common functions, cross-platformness, programmability and commonly used built-in objects. Detailed introduction: 1. Predefined, built-in objects are predefined in the JavaScript language, developers can use them directly without creating them themselves; 2. Methods and properties, built-in objects have many methods and properties, which define The behavior and functionality of objects, the Math object has static methods for mathematical operations, the Date object has methods for working with dates and times, and so on.
- Front-end Q&A 908 2023-11-09 13:56:55
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- What are the built-in objects of Vue?
- Vue's built-in objects include Vue, Vue instance, data, el, options, parent, root, children, slots, scopedSlots, refs, isServer, attrs and listeners. Vue.js is a progressive JavaScript framework for building user interfaces. In Vue.js, there are some built-in objects or global APIs that can be used to create and manage Vue applications.
- Front-end Q&A 1533 2023-11-08 16:52:16
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- What is the difference between null and undefined
- The difference between null and undefined is: 1. Semantic meaning; 2. Usage scenarios; 3. Comparison with other values; 4. Relationship with global variables; 5. Relationship with function parameters; 6. Nullability check; 7. Performance considerations; 8. Performance in JSON serialization; 9. Relationship with types. Detailed introduction: 1. Semantic meaning, null usually means knowing that this variable will not have any valid object value, while undefined usually means that the variable has not been assigned a value, or the object does not have this attribute; 2. Usage scenarios, etc.
- Front-end Q&A 1650 2023-11-08 16:43:23
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- What are jsp built-in objects
- JSP built-in objects refer to some predefined objects in JSP. Can be used directly in the page, these built-in objects provide many useful functions and properties, making it easier for developers to process and manipulate data. Common built-in objects in JSP include request object, response object, out object, session object, application object, config object, pageContext object, exception object, etc.
- Front-end Q&A 943 2023-11-03 14:36:22
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- What are built-in objects
- Built-in objects are objects that are predefined in a programming language. These objects usually provide some useful functions and methods to make programming more convenient for developers. In many programming languages there are built-in objects that can be used directly without additional imports or instantiations. Common built-in objects: 1. Math object; 2. Date object; 3. Array object; 4. String object; 5. RegExp object. Different programming languages may also provide other built-in objects to handle file operations and network communications.
- Front-end Q&A 1455 2023-11-03 14:24:22
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- Why prevent events from bubbling up
- The reasons for preventing event bubbling are to avoid unnecessary event processing, control the scope of event propagation, prevent event conflict and interference, and improve user experience. Detailed introduction: 1. Avoid unnecessary event processing. When an event is triggered on a child element, if the event continues to bubble up to the parent element or ancestor element, multiple event handling functions may be triggered. If these event handling functions All performing similar operations may lead to repeated calculations or processing, which wastes resources. By preventing events from bubbling, unnecessary event processing can be avoided, and the performance and efficiency of the code can be improved, etc.
- Front-end Q&A 1142 2023-11-02 17:54:45
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- Why is the event bubbling triggered twice?
- The reason why event bubbling is triggered twice may be due to the binding method of the event processing function, the event delegation, the methods of the event object, the nested relationship of the events, etc. Detailed introduction: 1. How to bind event processing functions. When binding event processing functions, you can use the "addEventListener" method to bind events. If the same type of event processing functions are bound to the same element multiple times, Then during the event bubbling stage, these event processing functions will be triggered in sequence, causing the event to be triggered multiple times; 2. Event delegation is a front-end development technique and so on.
- Front-end Q&A 1446 2023-11-02 17:49:01
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- Why can't capture events be prevented?
- The failure to prevent capturing events may be caused by the execution timing of the event processing function, the binding method of the event processing function, the method of the event object or event delegation, etc. Detailed introduction: 1. The execution timing of the event processing function. In the event capture phase and the event bubbling phase, the browser will execute the corresponding event processing function in sequence. If you try to prevent the propagation of the event in the event processing function in the event capture phase, but If there is no corresponding processing in the event processing function in the event bubbling stage, the event will continue to bubble; 2. The binding method of the event processing function, etc.
- Front-end Q&A 1122 2023-11-02 17:36:18
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- What does promise mean?
- Promise is a programming pattern for handling asynchronous operations. It is an object that represents the final completion or failure of an asynchronous operation. It can be seen as a commitment to asynchronous operations. It can better manage and organize asynchronous code. , making the code more readable and maintainable. Promise objects have three states: pending, fulfilled and rejected. The core idea of Promise is to separate asynchronous operations from callback functions and express the dependencies between asynchronous operations through chain calls.
- Front-end Q&A 1945 2023-11-02 17:30:17
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- What are the functions of promise?
- The functions of promises include solving the callback hell problem, better handling asynchronous operations, simplifying error handling of asynchronous operations, executing multiple asynchronous operations in parallel, controlling the execution flow of asynchronous operations, and supporting serial execution of asynchronous operations. Detailed introduction: 1. Solve the problem of callback hell. In the traditional callback function method, the nesting of multiple asynchronous operations will lead to poor readability and maintainability of the code, forming callback hell. Promise calls through chaining way to connect asynchronous operations in order to make the code clearer and easier to understand, etc.
- Front-end Q&A 1674 2023-11-02 17:22:59
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- In what scenarios is promise used?
- Promises are used in scenarios such as asynchronous requests, timers, animation effects, parallel execution of multiple asynchronous operations, error handling of asynchronous operations, and complex asynchronous operation process control. Detailed introduction: 1. Asynchronous requests. In front-end development, asynchronous requests are often required, such as sending HTTP requests to obtain data. Promise can be used to better handle these asynchronous requests, and asynchronous operations can be expressed more clearly through Promise's chain calls. The dependencies between; 2. Timer, in front-end development, timing operations are often required, etc.
- Front-end Q&A 1713 2023-11-02 17:14:17
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