Recursively walk and transform EcmaScript AST
npm install rocamboleRecursively walk and add extra information/helpers to Esprima / Mozilla
SpiderMonkey Parser API compatible AST.
The main difference between other tools is that it also keeps information about
tokens and white spaces and it is meant to be used to transform the tokens and
not the string values itself.
This library is specially useful for non-destructive AST manipulation.
This module was heavily inspired by
node-falafel and
node-burrito but I needed more
information than what is currently available on falafel (specially about
tokens, empty lines and white spaces) and also needed to do the node traversing
on the opposite order (start from leaf nodes). The amount of changes required
to introduce the new features and the differences on the concept behind the
tool justified a new project.
It was created mainly to be used on
esformatter.
Besides all the regular tokens returned by esprima we also add a few more
that are important for non-destructive transformations:
* WhiteSpace
- Can store multiple white spaces (tabs are considered white space, line
breaks not). Important if you want to do non-destructive replacements that
are white-space sensitive.
- Multiple subsequent white spaces are treated as a single token.
* LineBreak
* LineComment
* BlockComment
It's way easier to rebuild the JS string if the tokens already have line breaks
and comments. It's also easier to identify if previous/next/current token is a
LineBreak or Comment (sometimes needed for non-destructive transformations).
Rocambole structure might change in the future to keep the extraneous tokens
outside the tokens array and also add an option to toggle the behavior.
(issue #7)
Each Node have the following extra properties/methods:
- parent : Node|undefined
- toString() : string
- next : Node|undefined
- prev : Node|undefined
- depth : Number
- startToken : Token
- endToken : Token
Each token also have:
- prev : Token|undefined
- next : Token|undefined
BlockComment also have:
- originalIndent: String|undefined
To get a better idea of the generated AST structure try out
rocambole-visualize.
You should **treat the tokens as a linked list instead of reading theast.tokens array** (inserting/removing items from a linked list is very cheap
and won't break the loop). You should grab a reference to the node.startToken
and get token.next until you find the desired token or reach the end of the
program. To loop between all tokens inside a node you can do like this:
``js`
var token = node.startToken;
while (token !== node.endToken.next) {
doStuffWithToken(token);
token = token.next;
}
The method toString loops through all tokens between node.startToken andnode.endToken grabbing the token.raw (used by comments) or token.value
properties. To implement a method similar to falafel you can do
this:
`js`
function update(node, str){
var newToken = {
type : 'Custom', // can be anything (not used internally)
value : str
};
// update linked list references
if ( node.startToken.prev ) {
node.startToken.prev.next = newToken;
newToken.prev = node.startToken.prev;
}
if ( node.endToken.next ) {
node.endToken.next.prev = newToken;
newToken.next = node.endToken.next;
}
node.startToken = node.endToken = newToken;
}
I plan to create helpers as separate projects when possible.
- rocambole-token: helpers for token manipulation/traversal
- rocambole-node: helpers for node manipulation/traversal
- rocambole-whitespace: helpers for whitespace manipulation
- rocambole-linebreak: helpers for line break manipulation
- rocambole-indent: helpers for indentation
Parses a string and instrument the AST with extra properties/methods.
`js`
var rocambole = require('rocambole');
var ast = rocambole.parse(string);
console.log( ast.startToken );
// to get a string representation of all tokens call toString()
console.log( ast.toString() );
You can pass custom options as the second argument:
`js`
rocambole.parse(source, {
loc: true,
// custom options are forwarded to the rocambole.parseFn
ecmaFeatures: {
arrowFunctions: true
}
});
IMPORTANT: rocambole needs the range, tokens and comment info totrue
build the token linked list, so these options will always be set to .
Allows you to override the function used to parse the program. Defaults to
esprima.parse.
`js`
// espree is compatible with esprima AST so things should work as expected
var espree = require('espree');
rocambole.parseFn = espree.parse;
rocambole.parseContext = espree;
Sets the context (this value) of the parseFn. Defaults to esprima.
Sets the default options passed to parseFn.
`js`
// default values
rocambole.parseOptions = {
// we need range/tokens/comment info to build the tokens linked list!
range: true,
tokens: true,
comment: true
};
The moonwalk() starts at the leaf nodes and go down the tree until it reachesProgram
the root node (). Each node will be traversed only once.
`js`
rocambole.moonwalk(ast, function(node){
if (node.type == 'ArrayExpression'){
console.log( node.depth +': '+ node.toString() );
}
});
Traverse order:
`
Program [#18]
|-BlockStatement [#14]
| |-IfStatement [#12]
| | |-BynaryExpression [#9]
| | | |-Identifier [#4]
| | | -Literal [#5]-BlockStatement [#10]
| |
| | -ExpressionStatement [#6]-AssignmentExpression [#3]
| |
| | |-Identifier [#1 walk starts here]
| | -Literal [#2]-VariableDeclaration [#13]
|
| -VariableDeclarator [#11]-Literal [#8]
| |-Identifier [#7]
|
-ReturnStatement [#17]-Identifier [#15]
``
This behavior is very different from node-falafel and node-burrito.
It loops through all nodes on the AST starting from the root node (Program),node-falafel
similar to .
`js`
rocambole.walk(ast, function(node){
console.log(node.type);
});
Besides the regular unit tests we also use
istanbul to generate code coverage
reports, tests should have at least 95% code coverage for statements, branches
and lines and 100% code coverage for functions or travis build will fail.
We do not run the coverage test at each call since it slows down the
performnace of the tests and it also makes it harder to see the test results.
To execute tests and generate coverage report call npm test --coverage, fornpm test
regular tests just do .
Coverage reports are not committed to the repository since they will change at
each npm test --coverage` call.
MIT