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- What are the advantages and disadvantages of promises
- The advantages are: 1. Asynchronous operations are more readable, and the multiple steps of asynchronous operations are clearly organized to make the code more readable; 2. Callback hell is avoided, and multiple asynchronous operations are executed in sequence. , avoid nested calls; 3. Better error handling; 4. Support concurrent operations, which is very helpful for improving program performance and efficiency. The disadvantages are: 1. High learning costs; 2. Compatibility issues, different browsers have different levels of support for ES6; 3. Promises cannot be canceled; 4. Synchronization operations cannot be processed, etc.
- Front-end Q&A 2064 2023-11-02 15:18:14
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- What are the basic data types in Qt?
- Qt's basic data types include string types, numerical types, container types, time types, etc. Detailed introduction: 1. String type, QString is used to store and operate Unicode strings, QByteArray is used to store and operate byte arrays; 2. Numeric type, divided into integer type and floating point type; 3. Container type, QList is used QVector is used to store a dynamic array of a group of objects, QMap is used to store an associative array of key-value pairs, etc.
- Front-end Q&A 1685 2023-11-02 15:11:06
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- What are the basic data types in VHDL
- There are basic data types in VHDL such as bits, bit vectors, logic, integers, real numbers, physics, time, strings, enumerations, records, etc. Detailed introduction: 1. Bit, used to describe a single binary bit; 2. Bit vector, which can represent the value of multiple bits; 3. Logic, used to represent Boolean values; 4. Integer, used to represent integer values, which can be positive Integers, negative integers or zero; 5. Real numbers, used to represent values with decimal parts; 6. Physics, used to represent values with units; 7. Time, used to represent time values, which can represent a certain point in time or time intervals etc.
- Front-end Q&A 1876 2023-11-02 14:55:27
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- What are the differences between div and span?
- The differences are: 1. div is a block-level element, and span is an inline element; 2. div will automatically occupy a line, while span will not automatically wrap; 3. div is used to wrap larger structures and layouts, and span is used to wrap Text or other inline elements; 4. div can contain other block-level elements and inline elements, and span can contain other inline elements.
- Front-end Q&A 1773 2023-11-02 14:29:17
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- What does the bubbling event do?
- The functions of bubbling events are to realize page interaction, event processing, improve performance and optimize code structure, realize complex functions, and achieve special effects. Detailed introduction: 1. Realize page interaction. Through bubbling events, you can capture and respond to various interactive behaviors on the page. When the user clicks an element on the page, the click event can be tracked through bubbling events. And perform corresponding processing; 2. Implement event processing. In a web page, there is a hierarchical relationship between elements. When an event on an element is triggered, the bubbling event will be triggered layer by layer and so on.
- Front-end Q&A 1559 2023-11-01 17:08:34
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- What does bubbling event mean?
- A bubbling event means that in the browser, when an event occurs on an element, the event will be passed to the parent element in order from the inside to the outside until it is passed to the document root element. This propagation process is similar to The process of bubbles rising in water is similar, so it is called event bubbling. The bubbling event mechanism provides a convenient and flexible way to handle events, reducing the duplication of code, while also increasing the readability and maintainability of the code. You need to pay attention to terminating the propagation of events at the appropriate time to ensure Prevent unexpected results.
- Front-end Q&A 2125 2023-11-01 16:57:20
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- Why do we need event bubbling and capturing?
- Event bubbling is an event processing mechanism that is passed layer by layer from event source elements to the outside. Its significance is to simplify code, improve performance and implement event delegation. Event capture is an event processing mechanism opposite to event bubbling. Its significance is to preprocess events in advance, prevent event bubbling and implement custom event delegation. Event bubbling and capturing are two interdependent event processing mechanisms in js. Each has unique advantages and application scenarios. Through reasonable use, it can better organize and manage code, improve program performance and maintainability, and improve program performance and maintainability. Implement more flexible event handling.
- Front-end Q&A 879 2023-11-01 14:21:39
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- When to use event capture
- The situations where event capture is used include that the position of the target element is not fixed, events need to be preprocessed in advance, custom event delegation is required, and asynchronously loaded elements are processed, etc. Detailed introduction: 1. The position of the target element is not fixed. When the position of the target element is not fixed, the event cannot be processed through event bubbling, because the event bubbling is passed upward from the target element. If the position of the target element is not fixed, , the event handler cannot be accurately triggered; 2. The event needs to be preprocessed in advance, and sometimes some preprocessing operations need to be performed before the event is passed to the target element, etc.
- Front-end Q&A 1446 2023-11-01 14:13:56
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- What are the instructions for capturing events?
- Instructions for capturing events include "addEventListener()", "oncapture", "captureEvents()" and other methods. Detailed introduction: 1. The "addEventListener()" method is a standard method for adding event handlers. It supports capturing events by passing two parameters in the "addEventListener()" method. The first parameter is the event type, and the second parameter is the event type. The first parameter is the event handler; 2. "oncapture" and so on.
- Front-end Q&A 1194 2023-11-01 14:00:44
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- Why do events bubble up first before being captured?
- The reason is due to the order of event propagation and the mechanism of event processing. Event bubbling means that events propagate from the innermost element and propagate outward step by step until they reach the outermost element. The event capture starts from the outermost element and propagates inward step by step until it reaches the innermost element. During the event delivery process, the event first starts from the innermost element of the target element, then passes to the outer elements step by step, and finally reaches the document root node. By bubbling first and then capturing, events can be transmitted and processed on elements at different levels, improving the maintainability of the code.
- Front-end Q&A 769 2023-11-01 13:48:16
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- What events cannot be captured
- Events that cannot be captured include scroll events, window events, focus events, input events, and custom component events. Detailed introduction: 1. The scroll event is an event triggered when the user scrolls the web page. Due to the nature of scroll events, they cannot be processed in the event capture stage; 2. Window events refer to events related to the browser window, such as window resizing, closing, etc. These events are usually processed in the browser window itself, rather than Passed to the target element through the event stream; 3. Focus events refer to events triggered when an element gains or loses focus, etc.
- Front-end Q&A 790 2023-11-01 13:44:21
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- What functions does promise have?
- Promise functions include Promise constructor, then function, catch function, finally function, all function, race function, etc. Detailed introduction: 1. Promise constructor, which accepts a function as a parameter. This function has two parameters, namely resolve and reject; 2. then function, used to specify the callback function when the Promise state changes; 3. catch function, used The callback function when an error occurs in the specified Promise, etc.
- Front-end Q&A 1252 2023-11-01 13:40:16
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- What method is used to capture events?
- Event capture can be achieved using methods such as callback functions, observer pattern, event-driven programming, and third-party libraries or frameworks. Detailed description: 1. Callback function, the program monitors specific events by registering a callback function. When an event occurs, the system will automatically call the registered callback function to respond; 2. Observer mode, by defining a set of observers and targets The observer interface implements the event publishing and subscription mechanism; 3. Event-driven programming, the program monitors and processes events through the event loop, etc.
- Front-end Q&A 1208 2023-11-01 13:18:58
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- What does event capture do?
- The functions of event capture include conveniently obtaining target elements and contextual information, effectively preventing event bubbling, customizing event processing logic, and improving page response speed. Detailed introduction: 1. It is convenient to obtain the target element and contextual information. In the event capture phase, when an event occurs, the browser will start from the outermost element and search for elements associated with the event layer by layer until the target element is found. So far; 2. Effectively prevent event bubbling. In the event model, when an event occurs, it will be passed down layer by layer starting from the outermost element. This process is called event bubbling, etc.
- Front-end Q&A 1575 2023-11-01 13:16:39
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- How to display two divs side by side
- The methods are: 1. Set the two div elements to the "float:left;" attribute; 2. Use CSS's flex layout to easily display elements side by side; 3. Use CSS's grid layout to also display elements side by side.
- Front-end Q&A 1488 2023-11-01 11:36:59
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