32 lines
1.2 KiB
Markdown
32 lines
1.2 KiB
Markdown
---
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title: What is the difference between synchronous and asynchronous code in JavaScript?
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shortTitle: Synchronous vs asynchronous code
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type: question
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language: javascript
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tags: [function,promise]
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author: chalarangelo
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cover: pineapple-on-green
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excerpt: Understanding the differences between synchronous and asynchronous code is a crucial piece of knowledge for every web developer.
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dateModified: 2021-11-14T05:00:00-04:00
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---
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Synchronous code runs in sequence. This means that each operation must wait for the previous one to complete before executing.
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```js
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console.log('One');
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console.log('Two');
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console.log('Three');
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// LOGS: 'One', 'Two', 'Three'
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```
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Asynchronous code runs in parallel. This means that an operation can occur while another one is still being processed.
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```js
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console.log('One');
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setTimeout(() => console.log('Two'), 100);
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console.log('Three');
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// LOGS: 'One', 'Three', 'Two'
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```
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Asynchronous code execution is often preferable in situations where execution can be blocked indefinitely. Some examples of this are network requests, long-running calculations, file system operations etc. Using asynchronous code in the browser ensures the page remains responsive and the user experience is mostly unaffected.
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