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Philosophy
Philosophy (click to show)
Prior to SheetJS, APIs for processing spreadsheet files were format-specific. Third-party libraries either supported one format, or they involved a separate set of classes for each supported file type. Even though XLSB was introduced in Excel 2007, nothing outside of SheetJS or Excel supported the format.
To promote a format-agnostic view, js-xlsx starts from a pure-JS representation that we call the "Common Spreadsheet Format". Emphasizing a uniform object representation enables radical features like format conversion (e.g. reading an XLSX template and saving as XLS) and circumvents the "class trap". By abstracting the complexities of the various formats, tools need not worry about the specific file type!
A simple object representation combined with careful coding practices enables use cases in older browsers and in alternative environments like ExtendScript and Web Workers. It is always tempting to use the latest and greatest features, but they tend to require the latest versions of browsers, limiting usability.
Utility functions capture common use cases like generating JS objects or HTML. Most simple operations should only require a few lines of code. More complex operations generally should be straightforward to implement.
Excel pushes the XLSX format as default starting in Excel 2007. However, there are other formats with more appealing properties. For example, the XLSB format is spiritually similar to XLSX but files often tend up taking less than half the space and open much faster! Even though an XLSX writer is available, other format writers are available so users can take advantage of the unique characteristics of each format.