diff --git a/build/main.cjs b/build/main.cjs
index 6602499..81e69f3 100644
--- a/build/main.cjs
+++ b/build/main.cjs
@@ -52,6 +52,25 @@ function fnvHash(str) {
     return shash;
 }
 
+// Note that this pads zeros
+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;
+}
+
 /* globals WebAssembly */
 
 async function builder(code, options) {
@@ -83,6 +102,32 @@ async function builder(code, options) {
             "memory": memory
         },
         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.";
+                }
+                console.log("ERROR: ", code, errStr);
+                throw new Error(errStr);
+            },
+            showSharedRWMemory: function() {
+                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(ffjavascript.Scalar.fromArray(arr, 0x100000000));
+            },
             error: function(code, pstr, a,b,c,d) {
                 let errStr;
                 if (code == 7) {
@@ -133,7 +178,12 @@ async function builder(code, options) {
             options.logFinishComponent
         );
 
-    wc = new WitnessCalculator(memory, instance, sanityCheck);
+    if (typeof instance.exports.getVersion == 'function') {
+        // Only circom 2 WASMs implement versioning
+        wc = new WitnessCalculatorCircom2(instance, sanityCheck);
+    } else {
+        wc = new WitnessCalculatorCircom1(memory, instance, sanityCheck);
+    }
     return wc;
 
     function p2str(p) {
@@ -146,7 +196,7 @@ async function builder(code, options) {
         return String.fromCharCode.apply(null, bytes);
     }
 }
-class WitnessCalculator {
+class WitnessCalculatorCircom1 {
     constructor(memory, instance, sanityCheck) {
         this.memory = memory;
         this.i32 = new Uint32Array(memory.buffer);
@@ -172,6 +222,10 @@ class WitnessCalculator {
         this.sanityCheck = sanityCheck;
     }
 
+    circom_version() {
+        return 1;
+    }
+
     async _doCalculateWitness(input, sanityCheck) {
         this.instance.exports.init((this.sanityCheck || sanityCheck) ? 1 : 0);
         const pSigOffset = this.allocInt();
@@ -317,4 +371,141 @@ class WitnessCalculator {
     }
 }
 
+class WitnessCalculatorCircom2 {
+    constructor(instance, sanityCheck) {
+        this.instance = instance;
+
+        this.version = this.instance.exports.getVersion();
+        this.n32 = this.instance.exports.getFieldNumLen32();
+
+        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 = ffjavascript.Scalar.fromArray(arr, 0x100000000);
+
+        this.witnessSize = this.instance.exports.getWitnessSize();
+
+        this.sanityCheck = sanityCheck;
+    }
+    
+    circom_version() {
+        return this.instance.exports.getVersion();
+    }
+
+    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);
+        var input_counter = 0;
+        keys.forEach( (k) => {
+            const h = fnvHash(k);
+            const hMSB = parseInt(h.slice(0,8), 16);
+            const hLSB = parseInt(h.slice(8,16), 16);
+            const fArr = flatArray(input[k]);
+            for (let i=0; i<fArr.length; i++) {
+        const arrFr = 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);
+            input_counter++;
+        } catch (err) {
+            // console.log(`After adding signal ${i} of ${k}`)
+                    throw new Error(err);
+        }
+            }
+
+        });
+        if (input_counter < this.instance.exports.getInputSize()) {
+            throw new Error(`Not all inputs have been set. Only ${input_counter} out of ${this.instance.exports.getInputSize()}`);
+        }
+    }
+
+    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(fromArray32(arr));
+        }
+
+        return w;
+    }
+
+    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;
+    }
+
+}
+
 exports.WitnessCalculatorBuilder = builder;
diff --git a/js/utils.js b/js/utils.js
index 3e69d07..2f9ac33 100644
--- a/js/utils.js
+++ b/js/utils.js
@@ -45,3 +45,22 @@ export function fnvHash(str) {
     shash = '0'.repeat(n).concat(shash);
     return shash;
 }
+
+// Note that this pads zeros
+export 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;
+}
diff --git a/js/witness_calculator.js b/js/witness_calculator.js
index 243496f..dcd25b7 100644
--- a/js/witness_calculator.js
+++ b/js/witness_calculator.js
@@ -17,7 +17,7 @@ limitations under the License.
 
 */
 
-import { flatArray, fnvHash } from "./utils.js";
+import { flatArray, fnvHash, toArray32 } from "./utils.js";
 import { Scalar, F1Field } from "ffjavascript";
 
 export default async function builder(code, options) {
@@ -49,6 +49,32 @@ export default async function builder(code, options) {
             "memory": memory
         },
         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.";
+                }
+                console.log("ERROR: ", code, errStr);
+                throw new Error(errStr);
+            },
+            showSharedRWMemory: function() {
+                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(Scalar.fromArray(arr, 0x100000000));
+            },
             error: function(code, pstr, a,b,c,d) {
                 let errStr;
                 if (code == 7) {
@@ -99,7 +125,12 @@ export default async function builder(code, options) {
             options.logFinishComponent
         );
 
-    wc = new WitnessCalculator(memory, instance, sanityCheck);
+    if (typeof instance.exports.getVersion == 'function') {
+        // Only circom 2 WASMs implement versioning
+        wc = new WitnessCalculatorCircom2(instance, sanityCheck);
+    } else {
+        wc = new WitnessCalculatorCircom1(memory, instance, sanityCheck);
+    }
     return wc;
 
     function p2str(p) {
@@ -113,7 +144,7 @@ export default async function builder(code, options) {
     }
 };
 
-class WitnessCalculator {
+class WitnessCalculatorCircom1 {
     constructor(memory, instance, sanityCheck) {
         this.memory = memory;
         this.i32 = new Uint32Array(memory.buffer);
@@ -139,6 +170,10 @@ class WitnessCalculator {
         this.sanityCheck = sanityCheck;
     }
 
+    circom_version() {
+        return 1;
+    }
+
     async _doCalculateWitness(input, sanityCheck) {
         this.instance.exports.init((this.sanityCheck || sanityCheck) ? 1 : 0);
         const pSigOffset = this.allocInt();
@@ -284,5 +319,139 @@ class WitnessCalculator {
     }
 }
 
+class WitnessCalculatorCircom2 {
+    constructor(instance, sanityCheck) {
+        this.instance = instance;
+
+        this.version = this.instance.exports.getVersion();
+        this.n32 = this.instance.exports.getFieldNumLen32();
+
+        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 = Scalar.fromArray(arr, 0x100000000);
+
+        this.witnessSize = this.instance.exports.getWitnessSize();
+
+        this.sanityCheck = sanityCheck;
+    }
+    
+    circom_version() {
+        return this.instance.exports.getVersion();
+    }
+
+    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);
+        var input_counter = 0;
+        keys.forEach( (k) => {
+            const h = fnvHash(k);
+            const hMSB = parseInt(h.slice(0,8), 16);
+            const hLSB = parseInt(h.slice(8,16), 16);
+            const fArr = flatArray(input[k]);
+            for (let i=0; i<fArr.length; i++) {
+        const arrFr = 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);
+            input_counter++;
+        } catch (err) {
+            // console.log(`After adding signal ${i} of ${k}`)
+                    throw new Error(err);
+        }
+            }
+
+        });
+        if (input_counter < this.instance.exports.getInputSize()) {
+            throw new Error(`Not all inputs have been set. Only ${input_counter} out of ${this.instance.exports.getInputSize()}`);
+        }
+    }
+
+    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(fromArray32(arr));
+        }
+
+        return w;
+    }
+
+    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;
+    }
 
+}