In
computing, tree shaking is a
dead code elimination technique that is applied when optimizing code. Often contrasted with traditional single-library dead code elimination techniques common to minifiers, tree shaking eliminates unused functions from across the bundle by starting at the entry point and only including functions that may be executed.
It is succinctly described as "live code inclusion".
History
Dead code elimination in
dynamic languages is a much harder problem than in static languages. The idea of a "treeshaker" originated in
LISP
A lisp is a speech impairment in which a person misarticulates sibilants (, , , , , , , ). These misarticulations often result in unclear speech.
Types
* A frontal lisp occurs when the tongue is placed anterior to the target. Interdental lisping ...
in the 1990s. The idea is that all possible execution flows of a program can be represented as a tree of function calls, so that functions that are never called can be eliminated.
The algorithm was applied to
JavaScript in
Google Closure Tools and then to
Dart
Dart or DART may refer to:
* Dart, the equipment in the game of darts
Arts, entertainment and media
* Dart (comics), an Image Comics superhero
* Dart, a character from ''G.I. Joe''
* Dart, a ''Thomas & Friends'' railway engine character
* Dar ...
in the dart2js compiler also written by
Google, presented by Bob Nystrom in 2012
and described by the book ''Dart in Action'' by author Chris Buckett in 2013:
The next wave of popularity of the term is attributed to Rich Harris's Rollup project
How To Clean Up Your JavaScript Build With Tree Shaking
/ref> developed in 2015.
Relation to ECMAScript 6 modules
The popularity of tree shaking in JavaScript is based on the fact that in contrast to CommonJS modules, ECMAScript 6 module loading is static and thus the whole dependency tree can be deduced by statically parsing the syntax tree. Thus tree shaking becomes an easy problem. However, tree shaking does not only apply at the import/export level: it can also work at the statement level, depending on the implementation.
References
{{reflist
Compiler optimizations