ts-simple-ast/docs/manipulation/index.md

TypeScript compiler wrapper for AST navigation and code generation.

---
title: Manipulating the AST
---

## Manipulating the AST

Most information about manipulation can be found in the [Details](../details) section. This section only contains general information about manipulation.

### Replacing any node with new text

This can be achieved with the `.replaceWithText(...)` method that exists on any node.

#### Example

Given the following code:

```ts
let myVariable = Some.Property.Access.Expression;
```

You can replace the property access expression with new text by doing the following:

```ts
const originalInitializer = sourceFile.getVariableDeclarations()[0].getInitializerOrThrow();
const newInitializer = originalInitializer.replaceWithText("MyReference");
```

That will make the source file hold the following text:

```ts
let myVariable = MyReference;
```

Note that `originalInitializer` will be forgotten after calling `.replaceWithText(...)` on it—an error will be thrown if you try to use it.
You will have to use the new node returned by that method.

### Adding, inserting, and removing statements

Statements can be added, inserted, or removed from nodes with a body (ex. functions, methods, namespaces, source files).

```ts
// add statements
const statements = sourceFile.addStatements("console.log(5);\nconsole.log(6);");
// insert statements (index is the child index to insert at)
const statements = sourceFile.insertStatements(3, "console.log(5);\nconsole.log(6);");
// remove statements
sourceFile.removeStatements([1, 3]); // removes statements from index 1 to 3
sourceFile.removeStatement(1);       // removes statement at index 1
```

When adding or inserting, you can also write using a [code writer](code-writer):

```ts
functionDeclaration.addStatements(writer => {
    writer.write("if (true)").block(() => {
        writer.write("something;");
    });
});
```

### Inserting, replacing, and removing any text

In some scenarios, a simple to use API might not have been implemented. If you find that's the case, open an issue on GitHub.

In the meantime, you can insert, replace, and remove text using the following methods, but *generally you will want to avoid using these if possible*:

```ts
// insert text
sourceFile.insertText(0, "// some comment\n");
// replace text
sourceFile.replaceText([3, 7], "a"); // "// a comment\n"
// remove text
sourceFile.removeText([sourceFile.getPos(), sourceFile.getEnd()]);
```

These methods are also available on any node that has a body (functions, classes, enums, etc.)

#### **Warning**

If you use `insertText`, `replaceText`, or `removeText`, all previously navigated descendants of the node will be forgotten and not be available for use—an error will be thrown
if you try to use them. You will have to renavigate to those nodes.

For example:

```ts
let classDeclaration = sourceFile.addClass({ name: "MyClass" });
sourceFile.insertText(0, "// some comment\n");

// this will throw...
classDeclaration.getInstanceProperties();

// you'll need to get the reference again:
classDeclaration = sourceFile.getClass("MyClass")!;
```