How to generate AST(Abstract Syntax Tree) of javascript code?

Node.js / September 25, 2020 / TopCode / 0

Introduction

Abstract Syntax Tree or AST is syntactic tree representations of a code. Each node of the tree denotes a construct occurring in the source code. This is a fundamental part of the way a compiler works. The syntax is “abstract” as it does not represent every detail appearing in the real syntax, but rather just the structural or content-related details. Abstract Syntax Tree does not include unnecessary punctuation and delimiters (braces, parentheses, semicolons, etc.).

Lets create a program to generate Abstract Syntax Tree.

First You need to install a third-party library named as Esprima by following command.

npm install esprima

Code to generate Asbstract Syntax Tree of Javascript Code is as follows:

var esprima = require('esprima');
// source code for which we have to generate AST
var program = 'const foo = 22';

let ast = esprima.parseScript(program);
console.log(JSON.stringify(ast))

Output of above code is:

% node demo.js
{
  "type": "Program",
  "body": [
    {
      "type": "VariableDeclaration",
      "declarations": [
        {
          "type": "VariableDeclarator",
          "id": {
            "type": "Identifier",
            "name": "foo"
          },
          "init": {
            "type": "Literal",
            "value": 22,
            "raw": "22"
          }
        }
      ],
      "kind": "const"
    }
  ],
  "sourceType": "script"
}

esprima.parseScript() takes complete source code as string and then generates abstract syntax tree of the code.

Conclusion

If you want to make static parser tool then Abstract Syntax Tree is very crucial. Hope you understand concept of AST. Lets create your own and have fun.

#Happy Coding #TopCode

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