/ast-eval

Statically evaluate AST branches, return optimized tree.

Primary LanguageJavaScript

ast-eval Build Status experimental

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

  • Fold expressions

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

  • Fold arrays

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

  • Decompute object access (optionally)

    • a['x'] = 1 → a.x = 1

  • Fold strings

    • '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

NPM