docs.md

Some brief explorations of getStaticValue() from @eslint-community/eslint-utils (or in this case, the typed version from @typescript-eslint/utils". Intending to update this later with better examples (and code) once I get more time.

index.ts

import { analyze } from "@typescript-eslint/scope-manager";
import { parse } from "@typescript-eslint/typescript-estree";
import { ASTUtils, AST_NODE_TYPES } from "@typescript-eslint/utils";
import dedent from "dedent";

const getAstAndScopeManager = (code: string) => {
  const ast = parse(code, {
    range: true,
  });

  return [ast, analyze(ast, { sourceType: "script" })] as const;
};

[
  `"string";`, // { value: 'string'}
  "1;", // { value: 1 }
  "null;", // { value: null }
  "true;", // { value: true }
  "undefined;", // null
].forEach((code) => {
  const [ast, scopeManager] = getAstAndScopeManager(code);

  const node = ast.body[0];

  if (ASTUtils.isNodeOfType(AST_NODE_TYPES.ExpressionStatement)(node)) {
    const staticValue = ASTUtils.getStaticValue(
      node.expression,
      scopeManager.scopes[0]
    );
    console.log(staticValue);
  }
});

[
  // Same as above
  `const a = "string";`,
  `const a = 1;`,
  `const a = null;`,
  `const a = true;`,
  `const a = undefined;`,

  `const obj = { a: "string", b: 1, c: null, d: true, e: undefined };`, // null
  `const obj = { a: "string", b: 1, c: null, d: true };`, // { value: { a: 'string', b: 1, c: null, d: true } }
].forEach((code) => {
  const [ast, scopeManager] = getAstAndScopeManager(code);

  const variableDeclaration = ast.body[0];

  if (
    ASTUtils.isNodeOfType(AST_NODE_TYPES.VariableDeclaration)(
      variableDeclaration
    )
  ) {
    const init = variableDeclaration.declarations[0].init;

    if (init !== null) {
      const staticValue = ASTUtils.getStaticValue(init, scopeManager.scopes[0]);
      console.log(code, staticValue);
    }
  }
});

[
  dedent`
    const a = 1;
    const b = a;

    b;
  `, // { value: 1 }
  dedent`
    const a = 1;
    const b = a + 1;

    b;
  `, // { value: 2 }
].forEach((code) => {
  const [ast, scopeManager] = getAstAndScopeManager(code);

  const node = ast.body[2];

  if (ASTUtils.isNodeOfType(AST_NODE_TYPES.ExpressionStatement)(node)) {
    const staticValue = ASTUtils.getStaticValue(
      node.expression,
      scopeManager.scopes[0]
    );
    console.log(code, staticValue);
  }
});

[
  dedent`
    const objectA = { a: "string", b: 1, c: null, d: true };

    const objectB = { ...objectA, e: false };
  `, // { value: { a: 'string', b: 1, c: null, d: true, e: false } }
].forEach((code) => {
  const [ast, scopeManager] = getAstAndScopeManager(code);

  const variableDeclaration = ast.body[1];

  if (
    ASTUtils.isNodeOfType(AST_NODE_TYPES.VariableDeclaration)(
      variableDeclaration
    )
  ) {
    const init = variableDeclaration.declarations[0].init;

    console.log(init);

    if (init !== null) {
      const staticValue = ASTUtils.getStaticValue(init, scopeManager.scopes[0]);
      console.log(code, staticValue);
    }
  }
});