ast-eval

Statically evaluate expressions in AST, also known as constants folding. Useful for precompilation tasks.

Use

npm install --save ast-eval

var esprima = require('esprima');
var gen = require('escodegen').generate;
var astEval = require('ast-eval');

var ast = esprima.parse('[1, 2 === "2", 3+4*10, [2] === 2]');
ast = astEval(ast);

gen(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

• [x] Fold expressions

  • [x] Binary expressions: 1000 * 60 * 60 → 36e6
  • [x] Logical expressions: {a:1} && {b:2} → true
  • [x] Math expressions: Math.sin(Math.Pi / 2 ) → 1

• [x] Fold arrays

  • [x] Safe methods: [1,2,3,new Date].concat(4, [5], new Date) → [1,2,3,new Date,4,5, new Date]
  • [x] 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]

• [ ] Fold static globals (what’s that?)

• [x] Decompute object access (optionally)

  • [x] a['x'] = 1 → a.x = 1

• [x] Fold strings

  • [x] 'a b c'.split(' ') → ['a', 'b', 'c']

• [ ] Propagate constants

  • [ ] 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)'

• [ ] 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