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5 JavaScript Detection ¶

LibreJS considers a very strict subset of JavaScript to be acceptable for use in non-free scripts. This is meant to maximimize compatibility with websites that haven’t tried to be LibreJS compatible.

We consider modification of the document non-trivial. There isn’t much that javascript could do that we would consider trivial, for anything else a free software license would be required.

The criterion is as follows:

For each function definition:

• It must call only primitives.
• The number of conditionals and loops must be at most 3.
• It does not declare an array more than 50 elements long.
• It must not call itself

For the rest of the script, outside of function definitions:

• It must call only primitives and functions defined above in the page.
• The number of conditionals and loops must be at most 3.

"function" means anything executable that gets a name, including methods.

Allowed primitives exclude:

• eval()
• ajax
• calling methods with the square bracket notation
• altering the dom
• most other items found as methods of the ‘.window‘ object.