Exploring Abstract Syntax Tree (AST) manipulation to understand how obfuscation tools work.

The first step involves parsing JavaScript code into an AST structure:

let a,b=1;
// 注释
var obj = {
    "name":1+3*2,
      "func":function add(a,b){
      let a1=3;
      return a+b
    }
}
function add(a,v){
    return a+v;
}
let xx;
xx = 12;

Using Babel's parser and related utilities, we can reconstruct equivalent code:

let fs = require("fs");
let parser = require("@babel/parser");
let types = require("@babel/types");
let generator = require("@babel/generator").default;
let traverse = require("@babel/traverse").default;

let jscode = fs.readFileSync("./input.js", { encoding: "utf-8" });
let ast = parser.parse(jscode, { sourceType: "module" });

let one = types.variableDeclaration("let",[
    types.variableDeclarator(types.identifier("a"),null),
    types.variableDeclarator(types.identifier("b"),types.numericLiteral(120))
]);
console.log(generator(one).code);

let two = types.variableDeclaration("var",[
    types.variableDeclarator(types.identifier("obj"),types.objectExpression([
        types.objectProperty(types.stringLiteral("name"),types.binaryExpression("+",types.numericLiteral(1),types.binaryExpression("*",types.numericLiteral(3),types.numericLiteral(2)))),
        types.objectProperty(types.stringLiteral("func"),types.functionExpression(null,[types.identifier("a"),types.identifier("b")],types.blockStatement([
            types.variableDeclaration("let",[types.variableDeclarator(types.identifier("a1"),types.numericLiteral(3))]),
            types.returnStatement(types.binaryExpression("+",types.identifier("a"),types.identifier("b")))
        ])))
    ]))
]);
console.log(generator(two).code);

let three = types.functionDeclaration(types.identifier("add"),[types.identifier("a"),types.identifier("v")],types.blockStatement([types.returnStatement(types.binaryExpression("+",types.identifier("a"),types.identifier("v")))]));
console.log(generator(three).code);
let four = types.variableDeclaration("let",[types.variableDeclarator(types.identifier("xx"),null)]);
console.log(generator(four).code);
let five = types.expressionStatement(types.assignmentExpression("=",types.identifier("xx"),types.numericLiteral(12)));
console.log(generator(five).code);

One approach to obufscate code uses a switch-case structure where execution order is randomized:

function sw1(){
    traverse(newAst, {
        FunctionDeclaration(path) {
            let statments = path.node.body.body.map(function (v, i) {
                return { index: i, value: v }
            });
            let i = statments.length;
            while (i > 0) {
                let j = Math.floor(Math.random() * i--);
                [statments[i], statments[j]] = [statments[j], statments[i]]
            }
            let orderArr = [],cases = [];
            statments.map(function (v, i) {
                orderArr[v['index']] = i+1;
                let ca = [];
                ca.push(v["value"])
                if(!types.isReturnStatement(v['value'])){
                    ca.push(types.continueStatement(null))
                }
                cases.push(types.switchCase(types.numericLiteral(i+1),ca));
            });
            let switchStatement = types.switchStatement(types.unaryExpression("+",types.memberExpression(types.identifier("arr"),types.updateExpression("++",types.identifier("index")),true)),cases);
            let vardec = types.variableDeclaration('let', [types.variableDeclarator(types.identifier("arr"), types.callExpression(types.memberExpression(types.stringLiteral(orderArr.join("|")), types.identifier("split"), false), [types.stringLiteral("|")])),types.variableDeclarator(types.identifier("index"),types.numericLiteral(0))])
            let whileStatement = types.whileStatement(types.unaryExpression("!",types.unaryExpression("!",types.arrayExpression([]))),types.blockStatement([switchStatement]));
            path.get("body").replaceWith(types.blockStatement([vardec,whileStatement]));
        }
    })
}

A alternative method employs a more complex control flow obfuscaiton:

function pushArr(arr) {
    let rstr;
    while (true) {
        rstr = Math.random().toString(36).substring(2, 10);
        if (arr.indexOf(rstr) == -1) {
            arr.push(rstr);
            break
        }
    }
    return rstr;
}
function sw2() {
    traverse(newAst, {
        FunctionDeclaration(path) {
            let blockStatement = path.node.body;
            let bigA = [];
            pushArr(bigA)
            let lastIndex = blockStatement.body.length - 1;
            let createIndex = types.variableDeclaration("var", [types.variableDeclarator(types.identifier("index"), types.stringLiteral(bigA[0]))]);
            let cases = [];
            let index = 0;
            blockStatement.body.map(function (i, v) {
                let continueOrbreak = types.continueStatement(null);
                if (v == lastIndex) {
                    continueOrbreak = types.breakStatement(null);
                }
                if (types.isWhileStatement(i)) {
                    let continueOrbreak = types.continueStatement(null);
                    let test = i.test;
                    let body = i.body.body;
                    let start = index;
                    body.map(function (i, v) {
                        let swcase = types.switchCase(types.stringLiteral(bigA[index]), [i, types.expressionStatement(types.assignmentExpression("=", types.identifier("index"), types.stringLiteral(pushArr(bigA)))), continueOrbreak]);
                        cases.push(swcase);
                        index++
                    })

                    let express = types.expressionStatement(types.conditionalExpression(test, types.assignmentExpression("=", types.identifier("index"), types.stringLiteral(bigA[start])), types.assignmentExpression("=", types.identifier("index"), types.stringLiteral(pushArr(bigA)))));
                    let swcase = types.switchCase(types.stringLiteral(bigA[index]), [express, continueOrbreak]);
                    cases.push(swcase);
                } else {
                    let swcase = types.switchCase(types.stringLiteral(bigA[index]), [i, types.expressionStatement(types.assignmentExpression("=", types.identifier("index"), types.stringLiteral(pushArr(bigA)))), continueOrbreak]);
                    cases.push(swcase);
                }
                index++;
            })
            while (index > 0) {
                let j = Math.floor(Math.random() * index--);
                [cases[index], cases[j]] = [cases[j], cases[index]]
            }
            let switchCase = types.switchStatement(types.identifier("index"), cases);
            let whileStatement = types.whileStatement(types.unaryExpression("!", types.unaryExpression("!", types.arrayExpression([]))), types.blockStatement([switchCase, types.breakStatement(null)]))

            path.get("body").replaceWith(types.blockStatement([createIndex, whileStatement]));
        }
    });
}
sw2()

This transformation results in a complex control flow that makes reverse engineering harder:

var arg1 = '7D00060AB58C935689F6B166E65F46884E5F69AC';
var l = function () {
    var _0x5e8b26 = "3000176000856006061501533003690027800375";
    String['prototype']['hexXor'] = function (_0x4e08d8) {
        var _0x5a5d3b = '';
        for (var _0xe89588 = 0; _0xe89588 < this['length'] && _0xe89588 < _0x4e08d8['length']; _0xe89588 += 2) {
            var _0x401af1 = parseInt(this['slice'](_0xe89588, _0xe89588 + 2), "16");
            var _0x105f59 = parseInt(_0x4e08d8['slice'](_0xe89588, _0xe89588 + 2), "16");
            var _0x189e2c = (_0x401af1 ^ _0x105f59)['toString']("16");
            if (_0x189e2c['length'] == 1) {
                _0x189e2c = '\x30' + _0x189e2c;
            }
            _0x5a5d3b += _0x189e2c;
        }
        return _0x5a5d3b;
    };
    String['prototype']['unsbox'] = function () {
        var _0x4b082b = [15, 35, 29, 24, 33, 16, 1, 38, 10, 9, 19, 31, 40, 27, 22, 23, 25, 13, 6, 11, 39, 18, 20, 8, 14, 21, 32, 26, 2, 30, 7, 4, 17, 5, 3, 28, 34, 37, 12, 36];
        var _0x4da0dc = [];
        var _0x12605e = '';
        for (var _0x20a7bf = 0; _0x20a7bf < this['length']; _0x20a7bf++) {
            var _0x385ee3 = this[_0x20a7bf];
            for (var _0x217721 = 0; _0x217721 < _0x4b082b['length']; _0x217721++) {
                if (_0x4b082b[_0x217721] == _0x20a7bf + 1) {
                    _0x4da0dc[_0x217721] = _0x385ee3;
                }
            }
        }
        _0x12605e = _0x4da0dc['join']("");
        return _0x12605e;
    };
    var _0x23a392 = arg1['unsbox']();
    arg2 = _0x23a392['hexXor'](_0x5e8b26);
    return arg2;
};
console.log(l());