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esrefactor (BSD licensed) is a little helper library for ECMAScript refactoring.


With Node.js:

npm install esrefactor

In a browser, include first all the dependents:

<!-- esrefactor depends on these libraries -->
<script src="esprima.js"></src>
<script src="estraverse.js"></src>
<script src="escope.js"></src>
<script src="esrefactor.js"></src>


Before using the API, a context needs to be created:

var ctx = new esrefactor.Context(code);

where code is the source code.


An identifier, whether it is a variable, a function name, or a function parameter, can be identified using identify(). Example:

var ctx = new esrefactor.Context('var x = 42; y = x * 2; z = x / 2');
var id = ctx.identify(4);

The only argument to identify is the zero-based position index.

The return object has 3 (three) properties:

  • identifier: the syntax node associated with the position
  • declaration: the declaration syntax node for the identifier
  • references: an array of all identical references

If there is no declaration for the identifier (e.g. x = 42, global leak), then declaration will be null.

The resolution of the declaration syntax node and the references array take into account the identifier scope as defined in the official ECMAScript 5.1 Specification (ECMA-262).

Note that if there is no identifier in the given position index, identify() will return undefined.


An identifier can be renamed using rename(). All other identical references associated with that identifier will be renamed as well, again taking into account the proper identifier scope. Renaming works for variable declaration, function name, and function parameter.

For rename() to work, it needs to have the identification result (via identify) and the new name for the identifier.

var ctx = new esrefactor.Context('var x; x = 42');
var id = ctx.identify(4);
var code = ctx.rename(id, 'answer');

In the above example, code is var answer; answer = 42.