ast-eval
Statically evaluate expressions in AST, also known as constants folding. Useful for precompilation tasks.
Use
npm install --save ast-eval
var esprima = ;var gen = generate;var astEval = ; var ast = esprima;ast = ; ; //'[1, false, 43, false]'
API
preeval(Node, options) → Node
Evaluate expressions in a Node, return a new Node with optimized shorten expression nodes.
Features
-
Fold expressions
- Binary expressions:
1000 * 60 * 60
→36e6
- Logical expressions:
{a:1} && {b:2}
→true
- Math expressions:
Math.sin(Math.Pi / 2 )
→1
- Binary expressions:
-
Fold arrays
- Safe methods:
[1,2,3,new Date].concat(4, [5], new Date)
→[1,2,3,new Date,4,5, new Date]
- Unsafe methods:
[1,2,3].map(function(x){ return x*2})
→[2,4,6]
- Static methods:
Array.from([1, 2, 3], function(x){ return x*2; })
→[2,4,6]
- Prototype methods:
Array.prototype.slice.call([1,2,3], 1,2)
→[2]
- Safe methods:
-
Fold static globals (what’s that?)
-
Decompute object access (optionally)
-
a['x'] = 1
→a.x = 1
-
-
Fold strings
-
'a b c'.split(' ')
→['a', 'b', 'c']
-
-
- Simple flow analysis:
var x = 1; x + 2;
→3;
- Scope analysis
- Method substitution:
var slice = Array.prototype.slice; var x = [1,2,3]; var y = slice(x)'
- Simple flow analysis:
-
Fold loops
-
var x = []; for (var i = 0; i < 10; i++) {x[i] = 10*i;}
-
-
Fold proxy functions
-
Remove unused props
-
Undead code
- Empty isolated functions
- Remove unused variables (after enabling constants)
- Remove unused functions
- Remove unused properties
-
Fold clone-code
a.x
×3 →var _a = a; _a.x
-
Data-flow analysis
- Precall functions
- Substitute variables
-
Provide exports
-
Fold primitives
- new Array([1,2,3,...])
- [1,2,3,...]
-
Rearrange things
- Hoist functions (place after first use)
- Fold variable declarations
References
- List of compiler optimizations — ideas of folding.
- Substack’s static-eval — evaluate static expressions.
- esmangle