# Setting Default Token & Chain

### Overview

The initial destination chain and token are set with `dstChainId` and `dstToken` in the iframe URL. Both are plain, URL‑encoded strings (`dstChainId` is a chain ID; `dstToken` is an ERC‑20 address). If either value is invalid or the token isn’t available on that chain, the widget falls back to its built‑in defaults.

See [Supported Chains](/api-v1-reference/types.md#supported-chains)

#### Usage Example

```javascript
// In your JavaScript when configuring the widget:
const integratorId = "xxx";  // Your actual integrator ID
const dstChainId = "1"
const dstToken = "0x8fe815417913a93ea99049fc0718ee1647a2a07c";

const IFRAME_BASE_URI = "https://app.swapper.finance";
const iframe = document.getElementById("swapperFinanceWidget");  

// Build query string
const queryParams = new URLSearchParams({
  integratorId,
  dstChainId,
  dstToken
}).toString();

// Assign to iframe
if (iframe) {
  const iframeSrc = `${IFRAME_BASE_URI}?${queryParams}`;
  iframe.src = iframeSrc
  console.log("Swapper Finance Widget: URL configured with query parameters.");
  console.log("Full URL:", iframeSrc);
} else {
  console.error("Iframe element not found: please ensure its id is 'swapperFinanceWidget'.");
}

```


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