CODEWITHSUNDEEP
javascriptabstract-syntax-tree
jiyinyiyong
jiyinyiyong

Reputation: 4713

What is JavaScript AST, how to play with it?

Abstract Syntax Tree.. I always heard that compile to SpiderMonkey AST on Github.
So, is that a actual standard of JS syntax tree? And there's V8, is V8 using the same kind of AST?

How can I play with that?

Upvotes: 80

Views: 61027

Answers (5)

coderaiser
coderaiser

Reputation: 827

Abstract Syntax Tree (AST), is a tree representation of program source code.

There is a couple JavaScript AST standards:

Here is a list of JavaScript parsers:

You can find more parsers on astexplorer.net, most of them estree compatible.

While most parsers that supports estree can be easily replaced by each other, babel has very rich infrastructure needed to comfortable work with AST. It has:

  • handbook describing all the tools, and ways to use it.
  • @babel/traverse - maintains the overall tree state, and is responsible for replacing, removing, and adding nodes;
  • @babel/template - simplest way to create a AST-node from string.
  • @babel/types - contains builders and checkers of AST-nodes.

One of the simplest way to play with AST, is using putout, which is based on babel and supports simplified way of transforming JavaScript code with help of plugins API.

Here is example of removing DebuggerStatement node:

module.exports.replace = () => ({
    'debugger': '',
});

If you want switch places of variables, changing the way of declaration:

module.exports.replace = () => ({
    'let __a = __b': 'const __b = __a'
});

If you want transform this code into return x[0]:

for (const x of y) {
    return x;
}

You can use:

module.exports.replace = () => ({
    'for (const __a of __b) {return __a}': 'return __a[0]',
});

With help of putout you can make simplest transformation of JavaScript code without handling with AST directly.

Upvotes: 16

Rvach.Flyver
Rvach.Flyver

Reputation: 304

I know only of one specification of Javascript AST: https://github.com/estree/estree

It originated from publication of Dave Herman from Mozilla and since then evolved as community standard. So it should match SpiderMonkey at some degree but I'm not sure about V8 and JSC.

Would appreciate if someone could provide more information on the matter.

Upvotes: 1

prosti
prosti

Reputation: 46331

If you would like to try out the acron parser from professor Marijnh https://github.com/marijnh try out this link: https://astexplorer.net/

This is a tiny, fast JavaScript parser, written completely in JavaScript.

The above-mentioned JavaScript AST visualizer uses Esprima engine and has been also written in JavaScrpt.

JavaScript dominates in parsing AST because JavaScript engines are super optimized today. https://en.wikipedia.org/wiki/JavaScript_engine

SpiderMonkey AST standard of JS syntax tree? Is V8 using the same kind of AST?

Both of these web browser engines do have AST processing inside written in C++. This is why JavaScrpt code will run fast in most cases except for eval.

Upvotes: 4

cuixiping
cuixiping

Reputation: 25371

1.You can take a look at AST explorer. An online tool to explore the ASTs generated by more than 10 parsers. It is a good tool to learn AST tree of a language.
AST explorer source at Github.com.

enter image description here

2.Also you can paste your js code into JavaScript AST visualizer and click "show ast" button, you will see the AST visully.

demo js code:

function foo(d) {
  d += 3;
    return d+999
}
function bar(d) {
    return d*100
}

js ast demo

Upvotes: 73

salezica
salezica

Reputation: 76899

SpiderMonkey offers the parser api. This is probably the easiest way to get your hands on the syntax objects.

There's also open js-js parsers like Esprima (which is ECMAScript, really, but it's right up the alley)

Upvotes: 33

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