@alu0100953275/constant-folding/src/constant-folding.js

Constant Folding javascript code

// See https://github.com/babel/minify/tree/master/packages/babel-plugin-minify-constant-folding
const fs = require("fs");
const deb = require('../src/deb.js');
const escodegen = require("escodegen");
const espree = require("espree");
const estraverse = require("estraverse");

"use strict";

module.exports = constantFolding;

/**
 * 
 * @param {string} code A string of code to be fold
 * 
 * @description A function that with a code given do a constant folding and return it folded.
 * Fist it parse de code given to a ast node, then we can work with it 
 * using estraverse and then calling the fuction replaceByLiteral the code gets
 * folded in ast mode, then we regenerate the code with the new ast generated
 * 
 * @returns {string} Returns the code with constant folding
 */
function constantFolding(code/* , pattern */) {
  const t = espree.parse(code , { ecmaVersion: 6, loc: false });

  estraverse.traverse(t, {
    leave: function (n) {
      if ( n.type == "BinaryExpression" && 
           n.left.type == "Literal" && n.right.type == "Literal") 
          { replaceByLiteral(n); }
    //   if (n.type == "CallExpression" &&
    //       n.callee.property.name == "join") { replaceByLiteralOfJoin(n); }
    },
    });

    // deb(t);
    let c = escodegen.generate(t);
  
    return c
}

/**
 * A function that replace the node of a binary expression given by a literal of
 * the result itself
 * @param {node} n node of binary expression (ast)
 */
function replaceByLiteral(n) {
  n.type = "Literal";

  n.value = eval(`${n.left.raw}${n.operator}${n.right.raw}`);
  n.raw = String(n.value);

  
  delete n.left;
  delete n.right;
}
/**
 * A function that replace a join saving the result in a literal
 * 
 * @param {node} n 
 */
// function replaceByLiteralOfJoin(n) {
//   let param = n.arguments[0].raw;

//   let string = [];

//   for (elements of n.callee.object.elements) {
//     string.push(elements.raw);
//   }
  
//   n.type = "Literal";
//   n.value = eval(`[${string}].${n.callee.property.name}(${param})`);
//   n.raw = String(n.value);

//   delete n.range;
//   delete n.callee;
//   delete n.arguments;
// }