@alu0101051420/constant-folding/src/egg-constant-folding.js

Constant Folding javascript code

const estraverse = require("estraverse");

"use strict";

module.exports = eggConstantFolding;

/**
 * A function that does constant folding onto the code it receives
 * @param {string} code A string containing the code to do the constant folding on
 * @returns {string} Returns the resulting code
 */
function eggConstantFolding(ast) {
  const operations = ['+', '-', '/', '*'];

  estraverse.traverse(ast, {
    leave: function (n) {
      if (
        n.type === "apply" &&
        n.args.length === 2 &&
        operations.includes(n.operator.name) &&
        n.args[0].type === "value" && n.args[1].type === "value"
      ) {
        binaryConstantFolding(n);
      }
    },
    keys: {
      apply: ['operator', 'args'],
      property: ['operator', 'args'],
      word: [],
      value: [],
    }
  }
  );
  return ast;
}

/**
 * Does ConstantFolding on binaryExpression nodes. I.E. turns 2+3 into 5.
 * @param {Object} n an AST node representing a binaryExpression.
 */
function binaryConstantFolding(n) {
  n.type = "value";

  n.value = eval(`${n.args[0].value} ${n.operator.name} ${n.args[1].value}`);

  delete n.args;
  delete n.operator;
}