💢 Interview Questions: Event loop mechanism

#js #interview #eventLoop

Question: Give an explanatory note on the event loop mechanism.

answer:

The event loop mechanism mainly has the following processes:

🍉Synchronous tasks are executed on the main thread, forming an execution context stack.

🍓Once all synchronous tasks in the execution stack have been executed, the system will read the asynchronous tasks in the queue, such as Promise.then(), setTimeout, AJAX callbacks, etc.

🍆The asynchronous task will be added to the task queue

🥑Once the execution stack is cleared, the system checks the task queue. If it is not empty, the first task is taken out and placed on the execution stack for execution.

🥦The main thread repeats the process of alternating execution of the stack and queue, thereby realizing queued execution of threads.
The event loop allows synchronous tasks and asynchronous tasks to be executed alternately in the same thread, making full use of CPU resources. This is important for JavaScript that supports UI interaction and responsiveness.

🚳 Interview Questions: Ajax implementation

#js #interview #ajax

Implement an ajax request function that supports Promise:

🍣Send a request using the XMLHttpRequest object

🍛Initialize the open method, configure the request method and url

🍷Add onload and onerror callback functions

🧉onload determines whether the status code is within the range of 200–300 resolve, otherwise reject

🫘onerror directly reject

🥧After the request is successful, resolve returns response, and after failure, reject reports an error.

🥟Support options to configure request parameters and request body

🍱Returns a Promise object, which can be processed externally using then/catch

Analysis: Promise is used to encapsulate asynchronous ajax requests and achieve a synchronous programming style.

🚳 Interview Questions: JSONP cross-domain implementation

#js #interview #jsonp

Analysis: Create the script node script.src, set the callback function callbackName, parse the parameters and splice the URL, dynamically insert it into the body to implement JSONP cross-domain request, and return the Promise interface.

📵 Interview Questions: Implement deep cloning

#js #interview #deepClone

Analysis: Recursively implement deep cloning of objects and arrays, returning basic types directly, and reference types recursively call deep cloning hierarchically.

🚱 Interview Questions: Function currying

#js #interview #deepClone #patterns

Analysis: Currying of the add function is achieved by recursively calling a function that continues to accept parameters.

🚳 Interview Questions: Implement promise.all method

#js #interview #promise

Analysis: Use the Promise.all principle to synchronize the Promise state through the counter and result array.

📵 Interview Questions: Implement Instanceof

#js #interview #instanceof

The instanceof operator in JavaScript can be used to determine whether an object is an instance of another object. However, the instanceof operator has some limitations, such as:

🥫The instanceof operator can only determine objects directly connected to the prototype chain.
🌯The instanceof operator cannot detect objects with cyclic prototype chains.
Therefore, the above code provides a more general instanceof function that can determine the relationship between any two objects.

The implementation principle of this function is:

🍗The function instanceof receives two parameters: left and right.
🥞First, the code checks to see if the number of parameters is 2, and if not, throws an error.
🥚Next, the code checks whether the left operand left is null. If so, it returns false directly, because null cannot be an instance of any object.
🧀Then, the code checks whether the type of the left operand left is an object. If not, it returns false directly, because only objects can be instances of the constructor.
🥖Next, the code uses Object.getPrototypeOf() to obtain the prototype of the left operand left and assigns it to the variable proto.
🍞In a loop, the code continues to traverse proto’s prototype chain until proto is null.
🥐In the loop, the code checks whether the prototype of the right operand right is equal to the current proto. If they are equal, it means that the left operand left is an instance of the right operand right and returns true.
🍠If no matching prototype is found at the end of the loop, that is, proto is null, it means that the left operand left is not an instance of the right operand right, and false is returned.

🚱 Interview Questions: Implement a debounce anti-shake function

#js #interview #debounce