> For the complete documentation index, see [llms.txt](https://donedeal0.gitbook.io/superdiff/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://donedeal0.gitbook.io/superdiff/features/getcodediff.md).

# getCodeDiff

Compares two codes and returns a structured diff: lines first, then the tokens of each changed line. Whitespace is kept, so indentation changes are reported too.

```js
import { getCodeDiff } from "@donedeal0/superdiff";
```

{% hint style="info" %}
To diff files, read them first: `getCodeDiff(await previousFile.text(), await currentFile.text())`.
{% endhint %}

**FORMAT**

**Input**

```ts
  previousCode: string | null | undefined,
  currentCode: string | null | undefined,
```

**Output**

```ts
type CodeDiff = {
  type: "code";
  status: "added" | "deleted" | "equal" | "updated";
  diff: {
    value: string;
    previousValue?: string;
    line: number | null;
    previousLine: number | null;
    status: "added" | "deleted" | "equal" | "updated";
    diff?: {
      value: string;
      previousValue?: string;
      status: "added" | "deleted" | "equal" | "updated";
    }[];
  }[];
};
```

Lines start at 1. `line` is `null` if the line was deleted, `previousLine` is `null` if it was added. `diff` holds the token changes of an `updated` line.

**USAGE**

**Input**

```diff
getCodeDiff(
- "const MAX = 280;\n\nfunction preview(post) {\n  return post.body;\n}",
+ "const MAX_LENGTH = 320;\n\nfunction preview(post) {\n  const text = post.body;\n  return text.slice(0, MAX_LENGTH);\n}"
);
```

**Output**

```diff
{
      type: "code",
+     status: "updated",
      diff: [
        {
+         value: "const MAX_LENGTH = 320;",
+         previousValue: "const MAX = 280;",
          line: 1,
          previousLine: 1,
+         status: "updated",
          diff: [
            { value: "const", status: "equal" },
+           { value: " MAX_LENGTH", previousValue: " MAX", status: "updated" },
            { value: " =", status: "equal" },
+           { value: " 320", previousValue: " 280", status: "updated" },
            { value: ";", status: "equal" },
          ],
        },
        {
          value: "",
          previousValue: "",
          line: 2,
          previousLine: 2,
          status: "equal",
        },
        {
          value: "function preview(post) {",
          previousValue: "function preview(post) {",
          line: 3,
          previousLine: 3,
          status: "equal",
        },
        {
+         value: "  const text = post.body;",
+         previousValue: "  return post.body;",
          line: 4,
          previousLine: 4,
+         status: "updated",
          diff: [
+           { value: "  const", previousValue: "  return", status: "updated" },
+           { value: " text", status: "added" },
+           { value: " =", status: "added" },
            { value: " post", status: "equal" },
            { value: ".", status: "equal" },
            { value: "body", status: "equal" },
            { value: ";", status: "equal" },
          ],
        },
        {
+         value: "  return text.slice(0, MAX_LENGTH);",
          line: 5,
          previousLine: null,
+         status: "added",
        },
        {
          value: "}",
          previousValue: "}",
          line: 6,
          previousLine: 5,
          status: "equal",
        },
      ],
}
```