The key to optimizing JavaScript execution time is to reduce main thread blocking, reasonably control execution frequency, reduce DOM operations and utilize efficient data structures. 1. Split or move the time-consuming task to the Web Worker to avoid lag on the main thread; 2. Use anti-shake and throttling to control the trigger frequency of high-frequency events, such as resize, scroll, etc.; 3. Cache DOM status, batch update content, and give priority to DocumentFragment; 4. Use native methods (such as map, filter) and appropriate data structures (such as Set, Map), and consider typed arrays when processing big data. These methods can effectively improve page response speed and user experience.

JavaScript execution efficiency directly affects page response speed and user experience, especially when dealing with complex logic or large amounts of data. Optimizing execution time is not only about writing more "smart" code, but more importantly, avoiding unnecessary consumption.

Reduce main thread blockage

JavaScript runs on the main thread by default. Once there are time-consuming operations (such as large loops and complex calculations), the entire page will be stuck. The most direct optimization method is to break down the task or move it to a Web Worker to execute.

• Avoid long-running functions
• Use setTimeout or requestIdleCallback to perform tasks shards
• Leave the computing-intensive operations to the Web Worker

For example, if an operation that traverses an array of millions of levels will be obviously stuttered if placed in the main thread, use Worker to free up the main thread resources and keep the UI responsive.

Reasonable use of anti-shake and throttling

When user interaction events (such as resize, scroll, input) are frequently triggered, it is easy to cause performance problems. Controlling the execution frequency through debounce and throttle can effectively reduce the burden.

• Anti-shake is suitable for scenarios where "the last operation takes effect", such as the search box input prompt
• Throttle is suitable for fixed time to execute only once, such as rolling loading

For example: when the window is resized, the page is re-layouted. If you do not use anti-shake, each pixel change will trigger calculations, which will be very expensive. Adding 300ms anti-shake can alleviate this problem.

Avoid frequent DOM operations

DOM operation costs are high, and frequent reading and writing not only affects performance, but may also cause rearrangement and redrawing. The solution is to minimize visits and update content in batches.

• Try to use variables to cache DOM status instead of repeatedly querying
• Batch insert using DocumentFragment (DocumentFragment)
• When batch-modifying styles, you should prioritize switching class instead of setting style one by one.

For example, if you want to add multiple elements to the page, create a structure first and then insert it at once, which is much faster than inserting one at a time.

Utilize native methods and efficient data structures

Modern JavaScript engines have made a lot of optimizations to native methods, and internal implementations of methods such as map and filter are often faster than handwritten for loops. In addition, selecting the appropriate data structure according to actual needs can also improve efficiency.

• Priority to using Set/Map instead of object search
• Array operations avoid unnecessary traversals
• Consider using typed arrays (such as Uint8Array ) for large data sets

For example, if you want to determine whether a certain value exists in a bunch of data, using Set's has method is much faster than traversing the array to check each element.

Basically these key points. Optimizing JS execution time is not something that can be achieved overnight, but starting from small things and gradually improving it in combination with actual scenarios will often make the effect very obvious.

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