# Retain comment on first line
# Problem
When removing or replacing the first statement in a file, it is possible for leading comments at the top of the file to be removed (opens new window).
# Solution
To retain the leading comments during a transformation, the comments array on the statement's node must be copied to the next statement's node that will be at the top of the file.
# Bad Example
# Transform
export default function transformer(file, api) {
const j = api.jscodeshift;
return j(file.source)
.find(j.VariableDeclaration)
.replaceWith(
j.expressionStatement(j.callExpression(
j.identifier('foo'), []
)
)
)
.toSource();
};
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# In
// Comment on first line
const firstStatement = require('some-module');
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# Out
foo();
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# Good Example
# Transform
export default function transformer(file, api) {
const j = api.jscodeshift;
const root = j(file.source);
const getFirstNode = () => root.find(j.Program).get('body', 0).node;
// Save the comments attached to the first node
const firstNode = getFirstNode();
const { comments } = firstNode;
root.find(j.VariableDeclaration).replaceWith(
j.expressionStatement(j.callExpression(
j.identifier('foo'),
[]
))
);
// If the first node has been modified or deleted, reattach the comments
const firstNode2 = getFirstNode();
if (firstNode2 !== firstNode) {
firstNode2.comments = comments;
}
return root.toSource();
};
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# In
// Comment on first line
const firstStatement = require('some-module');
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# Out
// Comment on first line
foo();
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