@putout/printer

Printer

Prints Babel AST to readable JavaScript.

• ☝️ Similar to Recast, but simpler and easier in maintenance, since it supports only Babel.
• ☝️ As opinionated as Prettier, but has more user-friendly output and works directly with AST.
• ☝️ Like ESLint but works directly with Babel AST.
• ☝️ Easily extandable with help of Overrides.

Supports:

• ✅ ES2023;
• ✅ JSX;
• ✅ TypeScript;

Install

npm i @putout/printer

API

const {print} = require('@putout/printer');
const {parse} = require('@babel/parser');
const ast = parse('const a = (b, c) => {const d = 5; return a;}');

print(ast);

// returns
`
const a = (b, c) => {
    const d = 5;
    return a;
};
`;

Overrides

When you need to extend syntax of @putout/printer just pass a function which receives:

• path, Babel Path
• print, a function to output result of printing into token array;

When path contains to dashes __ and name, it is the same as: print(path.get('right')), and this is actually traverse(path.get('right')) shortened to simplify read and process.

Here is how you can override AssignmentPattern:

const ast = parse('const {a = 5} = b');

print(ast, {
    format: {
        indent: '    ',
    },
    visitors: {
        AssignmentPattern(path, {print}) {
            print(' /* [hello world] */= ');
            print('__right');
        },
    },
});

// returns
'const {a /* [hello world] */= 5} = b;\n';

print

Used in previous example print can be used for a couple purposes:

• to print string;
• to print node when object passed;
• to print node when string started with __;

print(ast, {
    visitors: {
        AssignmentPattern(path, {print, maybe}) {
            maybe.print.newline(path.parentPath.isCallExpression());
            print(' /* [hello world] */= ');
            print('__right');
        },
    },
});

maybe

When you need some condition use maybe. For example, to add newline only when parent node is CallExpression you can use maybe.print.newline(condition):

print(ast, {
    visitors: {
        AssignmentPattern(path, {print, maybe}) {
            maybe.print.newline(path.parentPath.isCallExpression());
            print(' /* [hello world] */= ');
            print('__right');
        },
    },
});

write

When are you going to output string you can use low-level function write:

print(ast, {
    visitors: {
        BlockStatement(path, {write}) {
            write('hello');
        },
    },
});

indent

When you need to add indentation use indent, for example when you output body, you need to increment indentation, and then decrement it back:

print(ast, {
    visitors: {
        BlockStatement(path, {write, indent}) {
            write('{');
            indent.inc();
            indent();
            write('some;');
            indent.dec();
            write('{');
        },
    },
});

traverse

When are you needing to traverse node, you can use traverse:

print(ast, {
    visitors: {
        AssignmentExpression(path, {traverse}) {
            traverse(path.get('left'));
        },
    },
});

This is the same as print('__left') but more low-level, and supports only objects.

License

MIT