The basic usage of "UglifyJS.TreeTransformer".

UglifyJS.TreeTransformer.js

const UglifyJS = require('uglify-js');

var symbolTable = {};
var binaryOperations = {
  "+": (x, y) => x + y,
  "-": (x, y) => x - y,
  "*": (x, y) => x * y
}
var constexpr = new UglifyJS.TreeTransformer(null, function(node) {
  if (node instanceof UglifyJS.AST_Binary) {
    if (Number.isInteger(node.left.value) && Number.isInteger(node.right.value)) {
      return new UglifyJS.AST_Number({
        value: binaryOperations[node.operator].call(this, 
          Number(node.left.value), 
          Number(node.right.value))
      });
    } else {
      return new UglifyJS.AST_Number({
        value: binaryOperations[node.operator].call(this, 
          Number(symbolTable[node.left.name].value), 
          Number(symbolTable[node.right.name].value))
      })
    }
  }

  if (node instanceof UglifyJS.AST_VarDef) {
    // AST_VarDef -> AST_SymbolVar;
    symbolTable[node.name.name] = node.value;
  }
});

var ast = UglifyJS.parse(`
  var x = 10 * 2 + 6;
  var y = 4 - 1 * 100;
  console.log(x + y);
`);

// transform and print
ast.transform(constexpr);
console.log(ast.print_to_string());