Printing TypeScript code from AST

.gitignore

node_modules

astPrinter.ts

import ts from 'typescript';

// Create a Printer
const printer = ts.createPrinter({
    newLine: ts.NewLineKind.LineFeed,
    removeComments: false,
    omitTrailingSemicolon: true
});

// Create a source file
const sourceFile = ts.createSourceFile(
    'someFileName.ts',
    '',
    ts.ScriptTarget.ESNext,
    /*setParentNodes*/ false,
    ts.ScriptKind.TS
);

/**
 * Outputs
 * export function add (x: number, y: number): number {
 *      return x + y;
 * }
 */

function makeAddFuntion() {
    const parameters: ReadonlyArray<ts.ParameterDeclaration> = [
        ts.createParameter(
            /* decorators */ undefined,
            /* modifiers */ undefined,
            /* dot dot token */ undefined,
            /* name */ ts.createIdentifier('x'),
            /* questionToken */ undefined,
            /* type */ ts.createKeywordTypeNode(ts.SyntaxKind.NumberKeyword)
        ),
        ts.createParameter(
            /* decorators */ undefined,
            /* modifiers */ undefined,
            /* dot dot token */ undefined,
            /* name */ ts.createIdentifier('y'),
            /* questionToken */ undefined,
            /* type */ ts.createKeywordTypeNode(ts.SyntaxKind.NumberKeyword)
        )
    ];

    const statements: ts.Statement[] = [
        ts.createReturn(
            ts.createBinary(
                ts.createIdentifier('x'),
                ts.SyntaxKind.PlusToken,
                ts.createIdentifier('y')
            )
        )
    ];

    return ts.createFunctionDeclaration(
        /* decorators */ undefined,
        /* modifiers */ [ts.createModifier(ts.SyntaxKind.ExportKeyword)],
        /* asteriskToken */ undefined,
        /* name */ 'add',
        /* typeParameters/ generics */ [],
        /* parameters */ parameters,
        /* returnType */ ts.createKeywordTypeNode(ts.SyntaxKind.NumberKeyword),
        ts.createBlock(statements, /*multiline*/ true)
    );
}

/**
 * Outputs
 * function add (x: number, y: number): number {
 *      return x + y;
 * }
 */

function makeMultiplyFuntion() {
    const parameters: ReadonlyArray<ts.ParameterDeclaration> = [
        ts.createParameter(
            /* decorators */ undefined,
            /* modifiers */ undefined,
            /* dot dot token */ undefined,
            /* name */ ts.createIdentifier('x'),
            /* questionToken */ undefined,
            /* type */ ts.createKeywordTypeNode(ts.SyntaxKind.NumberKeyword)
        ),
        ts.createParameter(
            /* decorators */ undefined,
            /* modifiers */ undefined,
            /* dot dot token */ undefined,
            /* name */ ts.createIdentifier('y'),
            /* questionToken */ undefined,
            /* type */ ts.createKeywordTypeNode(ts.SyntaxKind.NumberKeyword)
        )
    ];

    const statements: ts.Statement[] = [
        ts.createReturn(
            ts.createBinary(
                ts.createIdentifier('x'),
                ts.SyntaxKind.AsteriskToken,
                ts.createIdentifier('y')
            )
        )
    ];

    return ts.createFunctionDeclaration(
        /* decorators */ undefined,
        /* modifiers */ [ts.createModifier(ts.SyntaxKind.ExportKeyword)],
        /* asteriskToken */ undefined,
        /* name */ 'multiply',
        /* typeParameters/ generics */ [],
        /* parameters */ parameters,
        /* returnType */ ts.createKeywordTypeNode(ts.SyntaxKind.NumberKeyword),
        ts.createBlock(statements, /*multiline*/ true)
    );
}

// Update the source file statements
sourceFile.statements = ts.createNodeArray([makeAddFuntion(), makeMultiplyFuntion()]);

// Print the new code
console.log(printer.printFile(sourceFile));

package.json

{
    "name": "printing-ts-ast",
    "private": true,
    "scripts": {
        "start": "ts-node --project tsconfig.json astPrinter.ts"
    },
    "dependencies": {
        "ts-node": "^8.1.0",
        "typescript": "^3.4.3"
    }
}

tsconfig.json

{
    "compilerOptions": {
        "target": "esnext",
        "module": "commonjs",
        "strict": true,
        "noImplicitAny": true,
        "strictNullChecks": true,
        "moduleResolution": "node",
        "noUnusedLocals": true,
        "noUnusedParameters": true,
        "esModuleInterop": true,
        "noErrorTruncation": true
    }
}