diff --git a/wasm/tester.js b/wasm/tester.js
new file mode 100644
index 0000000..1c0b55d
--- /dev/null
+++ b/wasm/tester.js
@@ -0,0 +1,198 @@
+const chai = require("chai");
+const assert = chai.assert;
+
+const fs = require("fs");
+var tmp = require("tmp-promise");
+const path = require("path");
+
+const util = require("util");
+const exec = util.promisify(require("child_process").exec);
+
+const loadR1cs = require("r1csfile").load;
+const ZqField = require("ffjavascript").ZqField;
+
+module.exports = wasm_tester;
+
+async function  wasm_tester(circomInput, _options) {
+
+    assert(await compiler_above_version("2.0.0"),"Wrong compiler version. Must be at least 2.0.0");
+    
+    tmp.setGracefulCleanup();
+
+    const dir = await tmp.dir({prefix: "circom_", unsafeCleanup: true });
+
+    //console.log(dir.path);
+
+    const baseName = path.basename(circomInput, ".circom");
+    const options = Object.assign({}, _options);
+
+    options.wasm = true;
+
+    options.sym = true;
+    options.json = options.json || false; // costraints in json format
+    options.r1cs = true;
+    options.output = dir.path;
+
+    await compile(circomInput, options);
+
+    const utils = require("./utils");
+    const WitnessCalculator = require("./witness_calculator");
+
+    const wasm = await fs.promises.readFile(path.join(dir.path, baseName+"_js/"+ baseName + ".wasm"));
+
+    const wc = await WitnessCalculator(wasm);
+
+    return new WasmTester(dir, baseName, wc);
+}
+
+async function compile (fileName, options) {    
+    var flags = "--wasm ";
+    if (options.sym) flags += "--sym ";
+    if (options.r1cs) flags += "--r1cs ";
+    if (options.json) flags += "--json ";
+    if (options.output) flags += "--output " + options.output + " ";
+    console.log(circom + flags + fileName);
+    
+    await exec("circom " + flags + fileName);
+}
+    
+class WasmTester {
+
+    constructor(dir, baseName, witnessCalculator) {
+        this.dir=dir;
+        this.baseName = baseName;
+        this.witnessCalculator = witnessCalculator;
+    }
+
+    async release() {
+        await this.dir.cleanup();
+    }
+
+    async calculateWitness(input, sanityCheck) {
+        return await this.witnessCalculator.calculateWitness(input, sanityCheck);
+    }
+
+    async loadSymbols() {
+        if (this.symbols) return;
+        this.symbols = {};
+        const symsStr = await fs.promises.readFile(
+            path.join(this.dir.path, this.baseName + ".sym"),
+            "utf8"
+        );
+        const lines = symsStr.split("\n");
+        for (let i=0; i<lines.length; i++) {
+            const arr = lines[i].split(",");
+            if (arr.length!=4) continue;
+            this.symbols[arr[3]] = {
+                labelIdx: Number(arr[0]),
+                varIdx: Number(arr[1]),
+                componentIdx: Number(arr[2]),
+            };
+        }
+    }
+
+    async loadConstraints() {
+        const self = this;
+        if (this.constraints) return;
+        const r1cs = await loadR1cs(path.join(this.dir.path, this.baseName + ".r1cs"),true, false);
+        self.F = new ZqField(r1cs.prime);
+        self.nVars = r1cs.nVars;
+        self.constraints = r1cs.constraints;
+    }
+
+    async assertOut(actualOut, expectedOut) {
+        const self = this;
+        if (!self.symbols) await self.loadSymbols();
+
+        checkObject("main", expectedOut);
+
+        function checkObject(prefix, eOut) {
+
+            if (Array.isArray(eOut)) {
+                for (let i=0; i<eOut.length; i++) {
+                    checkObject(prefix + "["+i+"]", eOut[i]);
+                }
+            } else if ((typeof eOut == "object")&&(eOut.constructor.name == "Object")) {
+                for (let k in eOut) {
+                    checkObject(prefix + "."+k, eOut[k]);
+                }
+            } else {
+                if (typeof self.symbols[prefix] == "undefined") {
+                    assert(false, "Output variable not defined: "+ prefix);
+                }
+                const ba = actualOut[self.symbols[prefix].varIdx].toString();
+                const be = eOut.toString();
+                assert.strictEqual(ba, be, prefix);
+            }
+        }
+    }
+
+    async getDecoratedOutput(witness) {
+        const self = this;
+        const lines = [];
+        if (!self.symbols) await self.loadSymbols();
+        for (let n in self.symbols) {
+            let v;
+            if (utils.isDefined(witness[self.symbols[n].varIdx])) {
+                v = witness[self.symbols[n].varIdx].toString();
+            } else {
+                v = "undefined";
+            }
+            lines.push(`${n} --> ${v}`);
+        }
+        return lines.join("\n");
+    }
+
+    async checkConstraints(witness) {
+        const self = this;
+        if (!self.constraints) await self.loadConstraints();
+        for (let i=0; i<self.constraints.length; i++) {
+            checkConstraint(self.constraints[i]);
+        }
+
+        function checkConstraint(constraint) {
+	    
+            const F = self.F;
+            const a = evalLC(constraint[0]);
+            const b = evalLC(constraint[1]);
+            const c = evalLC(constraint[2]);
+            assert (F.isZero(F.sub(F.mul(a,b), c)), "Constraint doesn't match");
+        }
+
+        function evalLC(lc) {
+            const F = self.F;
+            let v = F.zero;
+            for (let w in lc) {
+                v = F.add(
+                    v,
+                    F.mul( lc[w], witness[w] )
+                );
+            }
+            return v;
+        }
+    }
+
+}
+
+function version_to_list ( v ) {
+    return v.split(".").map(function(x) {
+	return parseInt(x, 10);
+    });
+}
+
+function check_versions ( v1, v2 ) {
+    //check if v1 is newer than or equal to v2
+    for (let i = 0; i < v2.length; i++) {
+	if (v1[i] > v2[i]) return true;
+	if (v1[i] < v2[i]) return false;
+    }
+    return true;
+}
+
+async function compiler_above_version(v) {
+    let output = await exec('circom --version').toString();
+    let compiler_version = version_to_list(output.slice(output.search(/\d/),-1));
+    vlist = version_to_list(v);
+    return check_versions ( compiler_version, vlist );
+}
+
diff --git a/wasm/utils.js b/wasm/utils.js
new file mode 100755
index 0000000..8c2f261
--- /dev/null
+++ b/wasm/utils.js
@@ -0,0 +1,53 @@
+const fnv = require("fnv-plus");
+
+module.exports.fnvHash = fnvHash;
+module.exports.toArray32 = toArray32;
+module.exports.fromArray32 = fromArray32;
+module.exports.flatArray = flatArray;
+
+function toArray32(s,size) {
+    const res = []; //new Uint32Array(size); //has no unshift
+    let rem = BigInt(s);
+    const radix = BigInt(0x100000000);
+    while (rem) {
+        res.unshift( Number(rem % radix));
+        rem = rem / radix;
+    }
+    if (size) {
+	var i = size - res.length;
+	while (i>0) {
+	    res.unshift(0);
+	    i--;
+	}
+    }
+    return res;
+}
+
+function fromArray32(arr) { //returns a BigInt
+    var res = BigInt(0);
+    const radix = BigInt(0x100000000);
+    for (let i = 0; i<arr.length; i++) {
+        res = res*radix + BigInt(arr[i]);
+    }
+    return res;
+}
+
+function flatArray(a) {
+    var res = [];
+    fillArray(res, a);
+    return res;
+
+    function fillArray(res, a) {
+        if (Array.isArray(a)) {
+            for (let i=0; i<a.length; i++) {
+                fillArray(res, a[i]);
+            }
+        } else {
+            res.push(a);
+        }
+    }
+}
+
+function fnvHash(str) {
+    return fnv.hash(str, 64).hex();
+}
diff --git a/wasm/witness_calculator.js b/wasm/witness_calculator.js
new file mode 100755
index 0000000..fd14cc0
--- /dev/null
+++ b/wasm/witness_calculator.js
@@ -0,0 +1,227 @@
+const utils = require("./utils");
+
+module.exports = async function builder(code, options) {
+
+    options = options || {};
+
+    const wasmModule = await WebAssembly.compile(code);
+
+    let wc;
+
+    
+    const instance = await WebAssembly.instantiate(wasmModule, {
+        runtime: {
+            exceptionHandler : function(code) {
+                let errStr;
+                if (code == 1) {
+                    errStr= "Signal not found. ";
+                } else if (code == 2) {
+                    errStr= "Too many signals set. ";
+                } else if (code == 3) {
+                    errStr= "Signal already set. ";
+		} else if (code == 4) {
+                    errStr= "Assert Failed. ";
+		} else if (code == 5) {
+                    errStr= "Not enough memory. ";
+		} else {
+		    errStr= "Unknown error\n";
+                }
+		// get error message from wasm
+		errStr += getMessage();
+                throw new Error(errStr);
+            },
+	    showSharedRWMemory: function() {
+		printSharedRWMemory ();
+            }
+
+        }
+    });
+
+    const sanityCheck =
+        options
+//        options &&
+//        (
+//            options.sanityCheck ||
+//            options.logGetSignal ||
+//            options.logSetSignal ||
+//            options.logStartComponent ||
+//            options.logFinishComponent
+//        );
+
+    
+    wc = new WitnessCalculator(instance, sanityCheck);
+    return wc;
+
+    function getMessage() {
+        var message = "";
+	var c = instance.exports.getMessageChar();
+        while ( c != 0 ) {
+	    message += String.fromCharCode(c);
+	    c = instance.exports.getMessageChar();
+	}
+        return message;
+    }
+	
+    function printSharedRWMemory () {
+	const shared_rw_memory_size = instance.exports.getFieldNumLen32();
+	const arr = new Uint32Array(shared_rw_memory_size);
+	for (let j=0; j<shared_rw_memory_size; j++) {
+	    arr[shared_rw_memory_size-1-j] = instance.exports.readSharedRWMemory(j);
+	}
+	console.log(utils.fromArray32(arr));
+    }
+
+};
+
+class WitnessCalculator {
+    constructor(instance, sanityCheck) {
+        this.instance = instance;
+
+	this.version = this.instance.exports.getVersion();
+        this.n32 = this.instance.exports.getFieldNumLen32();
+
+//        Not needed
+//        this.instance.exports.getRawPrime();
+//        const arr = new Array(this.n32);
+//        for (let i=0; i<this.n32; i++) {
+//            arr[this.n32-1-i] = this.instance.exports.readSharedRWMemory(i);
+//        }
+//        this.prime = utils.fromArray32(arr);
+
+        this.witnessSize = this.instance.exports.getWitnessSize();
+
+        this.sanityCheck = sanityCheck;
+    }
+    
+    async _doCalculateWitness(input, sanityCheck) {
+	//input is assumed to be a map from signals to arrays of bigints
+        this.instance.exports.init((this.sanityCheck || sanityCheck) ? 1 : 0);
+        const keys = Object.keys(input);
+        keys.forEach( (k) => {
+            const h = utils.fnvHash(k);
+            const hMSB = parseInt(h.slice(0,8), 16);
+            const hLSB = parseInt(h.slice(8,16), 16);
+            const fArr = utils.flatArray(input[k]);
+            for (let i=0; i<fArr.length; i++) {
+		const arrFr = utils.toArray32(fArr[i],this.n32)
+		for (let j=0; j<this.n32; j++) {
+		    this.instance.exports.writeSharedRWMemory(j,arrFr[this.n32-1-j]);
+		}
+		try {
+                    this.instance.exports.setInputSignal(hMSB, hLSB,i);
+		} catch (err) {
+		    // console.log(`After adding signal ${i} of ${k}`)
+                    throw new Error(err);
+		}
+            }
+
+        });
+    }
+
+    async calculateWitness(input, sanityCheck) {
+
+        const w = [];
+
+        await this._doCalculateWitness(input, sanityCheck);
+
+        for (let i=0; i<this.witnessSize; i++) {
+            this.instance.exports.getWitness(i);
+	    const arr = new Uint32Array(this.n32);
+            for (let j=0; j<this.n32; j++) {
+            arr[this.n32-1-j] = this.instance.exports.readSharedRWMemory(j);
+            }
+            w.push(utils.fromArray32(arr));
+        }
+
+        return w;
+    }
+    
+
+    async calculateBinWitness(input, sanityCheck) {
+
+        const buff32 = new Uint32Array(this.witnessSize*this.n32);
+	const buff = new  Uint8Array( buff32.buffer);
+        await this._doCalculateWitness(input, sanityCheck);
+
+        for (let i=0; i<this.witnessSize; i++) {
+            this.instance.exports.getWitness(i);
+	    const pos = i*this.n32;
+            for (let j=0; j<this.n32; j++) {
+		buff32[pos+j] = this.instance.exports.readSharedRWMemory(j);
+            }
+        }
+
+	return buff;
+    }
+    
+
+    async calculateWTNSBin(input, sanityCheck) {
+
+        const buff32 = new Uint32Array(this.witnessSize*this.n32+this.n32+11);
+	const buff = new  Uint8Array( buff32.buffer);
+        await this._doCalculateWitness(input, sanityCheck);
+  
+	//"wtns"
+	buff[0] = "w".charCodeAt(0)
+	buff[1] = "t".charCodeAt(0)
+	buff[2] = "n".charCodeAt(0)
+	buff[3] = "s".charCodeAt(0)
+
+	//version 2
+	buff32[1] = 2;
+
+	//number of sections: 2
+	buff32[2] = 2;
+
+	//id section 1
+	buff32[3] = 1;
+
+	const n8 = this.n32*4;
+	//id section 1 length in 64bytes
+	const idSection1length = 8 + n8;
+	const idSection1lengthHex = idSection1length.toString(16);
+        buff32[4] = parseInt(idSection1lengthHex.slice(0,8), 16);
+        buff32[5] = parseInt(idSection1lengthHex.slice(8,16), 16);
+
+	//this.n32
+	buff32[6] = n8;
+
+	//prime number
+	this.instance.exports.getRawPrime();
+
+	var pos = 7;
+        for (let j=0; j<this.n32; j++) {
+	    buff32[pos+j] = this.instance.exports.readSharedRWMemory(j);
+        }
+	pos += this.n32;
+
+	// witness size
+	buff32[pos] = this.witnessSize;
+	pos++;
+
+	//id section 2
+	buff32[pos] = 2;
+	pos++;
+
+	// section 2 length
+	const idSection2length = n8*this.witnessSize;
+	const idSection2lengthHex = idSection2length.toString(16);
+        buff32[pos] = parseInt(idSection2lengthHex.slice(0,8), 16);
+        buff32[pos+1] = parseInt(idSection2lengthHex.slice(8,16), 16);
+
+	pos += 2;
+        for (let i=0; i<this.witnessSize; i++) {
+            this.instance.exports.getWitness(i);
+            for (let j=0; j<this.n32; j++) {
+		buff32[pos+j] = this.instance.exports.readSharedRWMemory(j);
+            }
+	    pos += this.n32;
+        }
+
+	return buff;
+    }
+
+}
+
+
+