49 lines
1.6 KiB
Markdown
49 lines
1.6 KiB
Markdown
|
# estree-walker
|
||
|
|
|
||
|
|
Simple utility for walking an [ESTree](https://github.com/estree/estree)-compliant AST, such as one generated by [acorn](https://github.com/marijnh/acorn).
|
||
|
|
|
||
|
|
|
||
|
|
## Installation
|
||
|
|
|
||
|
|
```bash
|
||
|
|
npm i estree-walker
|
||
|
|
```
|
||
|
|
|
||
|
|
|
||
|
|
## Usage
|
||
|
|
|
||
|
|
```js
|
||
|
|
var walk = require( 'estree-walker' ).walk;
|
||
|
|
var acorn = require( 'acorn' );
|
||
|
|
|
||
|
|
ast = acorn.parse( sourceCode, options ); // https://github.com/acornjs/acorn
|
||
|
|
|
||
|
|
walk( ast, {
|
||
|
|
enter: function ( node, parent, prop, index ) {
|
||
|
|
// some code happens
|
||
|
|
},
|
||
|
|
leave: function ( node, parent, prop, index ) {
|
||
|
|
// some code happens
|
||
|
|
}
|
||
|
|
});
|
||
|
|
```
|
||
|
|
|
||
|
|
Inside the `enter` function, calling `this.skip()` will prevent the node's children being walked, or the `leave` function (which is optional) being called.
|
||
|
|
|
||
|
|
Call `this.replace(new_node)` in either `enter` or `leave` to replace the current node with a new one.
|
||
|
|
|
||
|
|
Call `this.remove()` in either `enter` or `leave` to remove the current node.
|
||
|
|
|
||
|
|
## Why not use estraverse?
|
||
|
|
|
||
|
|
The ESTree spec is evolving to accommodate ES6/7. I've had a couple of experiences where [estraverse](https://github.com/estools/estraverse) was unable to handle an AST generated by recent versions of acorn, because it hard-codes visitor keys.
|
||
|
|
|
||
|
|
estree-walker, by contrast, simply enumerates a node's properties to find child nodes (and child lists of nodes), and is therefore resistant to spec changes. It's also much smaller. (The performance, if you're wondering, is basically identical.)
|
||
|
|
|
||
|
|
None of which should be taken as criticism of estraverse, which has more features and has been battle-tested in many more situations, and for which I'm very grateful.
|
||
|
|
|
||
|
|
|
||
|
|
## License
|
||
|
|
|
||
|
|
MIT
|