babel-import-util

Makes it easier for a babel plugin to emit imported names. Key benefits:

- the output composes correctly with subsequent babel plugins, because we update Babel's understanding of the bindings
- redundant imports will be deduplicated automatically
- written in TypeScript

Usage by example:

If you want to rewrite:

``js
myTarget('hello world');
`

To:

`js
import { theMethod } from 'my-implementation';
theMethod('hello world');
`

Your plugin would look like this:

`js
function testTransform(babel) {
return {
visitor: {
Program: {
enter(path, state) {
// Always instantiate the ImportUtil instance at the Program scope
state.importUtil = new ImportUtil(babel, path);
},
},
CallExpression(path, state) {
let callee = path.get('callee');
if (callee.isIdentifier() && callee.node.name === 'myTarget') {
state.importUtil.replaceWith(callee, (i) =>
i.import(callee, 'my-implementation', 'theMethod')
);
}
},
},
};
}
`

API

`ts
import type { NodePath } from '@babel/traverse';
import type * as t from '@babel/types';

class ImportUtil {
/*
Replace target with the new node produced by your callback. Your
callback can use i.import to gain access to imported identifiers.

Example:

util.replaceWith(path, (i) =>
t.callExpression(i.import('my-library', 'someFunction'), [])
);
*/
replaceWith(
target: NodePath,
fn: (i: Importer) => R
): NodePath;

/*
Similar to replaceWith above, except instead of replacing the target
we will insert the new Node before or after it.
*/
insertAfter(
target: NodePath,
fn: (i: Importer) => R
): NodePath;
insertBefore(
target: NodePath,
fn: (i: Importer) => R
): NodePath;

// If needed, adds a bare import like:
// import "your-module";
importForSideEffect(moduleSpecifier: string): void;

// Remove an import specifier. If the removed specifier is
// the last one on the whole import statement, the whole
// statement is also removed.
//
// You can use "default" and "*" as exportedName to handle
// those special cases.
removeImport(moduleSpecifier: string, exportedName: string): void;

// Remove all imports from the given moduleSpecifier. Unlike
// removeImport(), this can also remove "bare" import statements
// that were purely for side effect.
removeAllImports(moduleSpecifier: string): void;

// Import the given value (if needed) and return an Identifier representing
// it.
// CAUTION: this is a lower-level API that leaves some of the reference
// safety up to you. It's better to use replaceWith, insertAfter, insertBefore,
// or mutate. But this can still be helpful in contexts where you're already
// planning to manage babel's scopes anyawy.
import(
// the spot at which you will insert the Identifier we return to you
target: NodePath,

// the path to the module you're importing from
moduleSpecifier: string,

// the name you're importing from that module. Use "default" for the default
// export. Use "*" for the namespace.
exportedName: string,

// Optional hint for helping us pick a name for the imported binding
nameHint?: string
): t.Identifier;
}
``