Can I prevent Babel from traversing code inserted by a plugin? - babeljs

Question

I'm building a plugin that inserts enterFunction() in front of every existing function call by calling path.insertBefore. So my code is transformed from:
myFunction();
To:
enterFunction();
myFunction();
The problem is that when I insert the node Babel once again traverses the inserted node. Here's the logging output:
'CallExpression', 'myFunction'
'CallExpression', 'enterFunction'
How can I prevent Babel from entering the enterFunction call expression and its children?
This is the code I'm currently using for my Babel plugin:
function(babel) {
return {
visitor: {
CallExpression: function(path) {
console.log("CallExpression", path.node.callee.name)
if (path.node.ignore) {
return;
}
path.node.ignore = true
var enterCall = babel.types.callExpression(
babel.types.identifier("enterFunction"), []
)
enterCall.ignore = true;
path.insertBefore(enterCall)
}
}
}
}

Answer 1

The Babel Handbook mentions the following section:
If your plugin needs to not run in a certain situation, the simpliest thing to do is to write an early return.
BinaryExpression(path) {
if (path.node.operator !== '**') return;
}
If you are doing a sub-traversal in a top level path, you can use 2 provided API methods:
path.skip() skips traversing the children of the current path. path.stop() stops traversal entirely.
outerPath.traverse({
Function(innerPath) {
innerPath.skip(); // if checking the children is irrelevant
},
ReferencedIdentifier(innerPath, state) {
state.iife = true;
innerPath.stop(); // if you want to save some state and then stop traversal, or deopt
}
});
In short, use path.skip() to skip traversing the children of the current path.
One application of this method is illustrated in this snippet using Visitors, CallExpression and skip():
export default function (babel) {
const { types: t } = babel;
return {
name: "ast-transform", // not required
visitor: {
CallExpression(path) {
path.replaceWith(t.blockStatement([
t.expressionStatement(t.yieldExpression(path.node))
]));
path.skip();
}
}
};
}