# Circuit ID

{% hint style="info" %}
To identify every circuit uniquely, users are required to provide a unique `cID` field for **`circuits`** entries inside the `build` field of the [circuit config file.](https://zefi.gitbook.io/circomjs/circuit-config-file) **They use this *****`cID`***** to get their respective circuit via the *****`getCircuit()`***** method** of [`CircomJS`](https://zefi.gitbook.io/circomjs/classes/circomjs).
{% endhint %}

For example, If we have a circuit by the name `multiplication.circom` inside our circuit's `inputDir` , then we would have to declare it in our [circuit config file](https://zefi.gitbook.io/circomjs/circuit-config-file) in the following manner:

{% code title="circuit.config.json" lineNumbers="true" %}

```
{
    "projectName": "circom-starter",
    "outputDir":"./out",
    "build": {
        "inputDir": "./circuits",
        "circuits": [
          {
              "cID": "mul",
              "fileName": "multiply.circom",
              "proofType": "groth16",
              "compilationMode": "wasm",
           }
        ]
    }
}
```

{% endcode %}

Now, when we want to get this [Circuit](https://zefi.gitbook.io/circomjs/classes/circuit) inside the Node JS program, we do the following:

{% code title="src/index.js" lineNumbers="true" %}

```javascript
const {CircomJS} = require("@zefi/circomjs")

const main = async() => {
    const circomjs = new CircomJS()
    const circuit =  circomjs.getCircuit("mul")   
    
    await circuit.compile()
}

main()
```

{% endcode %}

The following is taking place in the above code:

* We instantiate [`CircomJS`](#circomjs)
* We call the `getCircuit(cID)` method, where cID = "mul"
* CircomJS looks for a circuit that was tagged with a `cID` of `mul`  inside the [circuit config file](https://zefi.gitbook.io/circomjs/circuit-config-file) {check out [this](https://zefi.gitbook.io/circomjs/circuit-config-file/filename) section on the file path for the circuit is resolved. }
* It returns the respective circuit { throws an error if the circuit with that `cID` is not present }
* It builds the circuits { `await circuit.compile()` }.