Why can't the HTML file selector accept attribute effectively filter CSV files?

HTML file upload control accept attribute cannot effectively filter CSV files?

We often use it in web development<input type="file"> Elements allow users to select files to upload. accept attribute is used to limit selectable file types, improve user experience and security. However, this property does not always work perfectly. This article analyzes the problem that accept attribute cannot filter CSV files correctly and provides a solution.

Problem: The developer hopes to only allow uploading xls, xlsx and csv files, and uses the corresponding MIME type: application/vnd.ms-excel,application/vnd.openxmlformats-officedocument.spreadsheetml.sheet,text/csv . However, in actual tests, the xls and xlsx files are filtered normally, and the csv files are still available.

Code example (the original code example is missing, one is added here):

<input type="file" accept="application/vnd.ms-excel,application/vnd.openxmlformats-officedocument.spreadsheetml.sheet,text/csv">

Causes and solutions:

The accept attribute supports MIME type and file extension. Although the MIME type is more standardized, there are differences in browser support and parsing of MIME types, and some browsers may not be strict enough in identifying text/csv . To ensure cross-browser compatibility, it is recommended to use both MIME types and extensions.

Solution: Add .csv extension in the accept property:

<input type="file" accept=".xls,.xlsx,.csv,application/vnd.ms-excel,application/vnd.openxmlformats-officedocument.spreadsheetml.sheet,text/csv">

By adding .csv , the browser can more accurately identify and filter csv files, solve compatibility issues, and provide more reliable upload restrictions.

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