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coffeescript/documentation/sections/breaking_changes_default_values.md
Geoffrey Booth b28e398396 [CS2] Docs updates (#4536)
* Docs: named functions and function declarations

* No more prototypal `extends`; update docs and example

* More comprehensive documentation of the existential operator; closes #1631

* Better document operators, including `from`

* No fat arrow class methods anymore

* Destructuring shouldn’t say that default values are applied in case of undefined or null

* Spinoff generator and async functions into their own sections; reorder things so that the sections on functions come just before classes, and destructuring goes next to the operators (which discuss assignment)

* Rewrite “CoffeeScript 2” section, making it less practical and more explanatory; move practical info into “Usage”

* Update “Variable Scoping and Lexical Safety” section to remove incorrect reference to Ruby (fixes #2360), add missing details about the safety wrapper, add note about `let`/`const`.

* Updated browser compiler

* Updated docs

* Rewrite Literate CoffeeScript breaking changes

* Split apart the “Breaking Changes” and “Unsupported Features” sections into separate sidebar items and files

* Add example of `not in`, closes #3281

* Fix words in bold that should be in backticks

* Consolidate some breaking changes sections

* Add Node API documentation; closes #3551

* Move the chaining documentation out of the changelog into its own section
2017-05-05 19:44:11 -07:00

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Markdown

### Default values for function parameters and destructured elements
Per the [ES2015 spec regarding function default parameters](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/Default_parameters) and [destructuring default values](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Destructuring_assignment#Default_values), default values are only applied when a value is missing or `undefined`. In CoffeeScript 1.x, the default value would be applied in those cases but also if the value was `null`.
```
codeFor('breaking_change_function_parameter_default_values', 'f(null)')
```
```
codeFor('breaking_change_destructuring_default_values', 'a')
```