将 var 转化为 let

2024年11月10日

柏拉文

越努力，越幸运

一、认识

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二、实现

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const swc = require("@swc/core");

const { parseSync, printSync } = swc;

const parse = (sourceCode) => {
  try {
    const result = parseSync(sourceCode, {
      syntax: "ecmascript",
      jsx: false,
    });
    return result;
  } catch (error) {
    console.error("Error parsing source code:", error);
    return null;
  }
};

const visit = (ast, visitor) => {
  function traverse(node, parent) {
    if (!node || typeof node !== "object") return;

    if (visitor[node.type]) {
      visitor[node.type](node, parent);
    }

    for (const key in node) {
      if (!node.hasOwnProperty(key)) continue;

      const child = node[key];
      if (Array.isArray(child)) {
        child.forEach((c) => traverse(c, node));
      } else if (child && typeof child === "object") {
        traverse(child, node);
      }
    }
  }

  traverse(ast, null);
};

const find = (ast, type) => {
  const nodes = [];
  visit(ast, {
    [type]: (node) => {
      nodes.push(node);
    },
  });
  return nodes;
};

const replaceWith = (ast, targetNode, newNode) => {
  visit(ast, {
    [targetNode.type]: (node, parent) => {
      if (node === targetNode) {
        for (const key in parent) {
          if (parent.hasOwnProperty(key)) {
            if (Array.isArray(parent[key])) {
              parent[key] = parent[key].map((child) =>
                child === targetNode ? newNode : child
              );
            } else if (parent[key] === targetNode) {
              parent[key] = newNode;
            }
          }
        }
      }
    },
  });
};

async function main() {
  const sourceCode = `var a = 1; var b = 2; var c = () => { var d = 3; return d; };`;
  const ast = parse(sourceCode);

  if (!ast) return;

  // Find all VariableDeclaration nodes
  const variableDeclarations = find(ast, "VariableDeclaration");

  // Replace var with const
  variableDeclarations.forEach((node) => {
    if (node.kind === "var") {
      const newNode = { ...node, kind: "let" };
      replaceWith(ast, node, newNode);
    }
  });

  // Convert AST back to source code
  const newSourceCode = printSync(ast).code;
  console.log(newSourceCode);
}

main();