Question

我正在使用UglifyJS来解析，缩小和转换JS代码。我的目标之一是通过插入新的变量定义来转换AST。例如：

var x;
var y;
x = 1;
y = x;
x = 3;

我想插入一个新的变量定义＆＃34; var _x＆＃34;进入随机位置，例如在陈述之前＆＃34; y = x＆＃34;。转换后的代码应该是这样的：

var x;
var y;
x = 1;
var _x = x;
y = _x;
_x = 3;

我在UglifyJS中尝试过TreeTransformer。将符号引用更新为新的符号引用（x - ＆gt; _x）是没有问题的。但我不清楚使用TreeTransformer获取插入的正确位置。任何人都可以分享一些见解吗？一些代码示例会更好！

Answer 1

以下是我解决这个问题的方法。

var _ = require('lodash');
var path = require('path');
var Promise = require('bluebird');
var fs = Promise.promisifyAll(require('fs'));
var UglifyJS = require('uglify-js');

fs.readFileAsync(path.join(__dirname, 'source.js'), 'utf8').then(function (file) {
  var topLevel = UglifyJS.parse(file);

  var transformed = topLevel.transform(new UglifyJS.TreeTransformer(function (node, descend) {
    if (node instanceof UglifyJS.AST_Toplevel) {
      node = node.clone();

      // Add new variable declaration
      node.body.unshift(new UglifyJS.AST_Var({
        definitions: [
          new UglifyJS.AST_VarDef({
            name: new UglifyJS.AST_SymbolVar({
              name: '_x'
            })
          })
        ]
      }));

      // Replace existing assignment statement with new statements
      var index = _(node.body).findIndex(function (node) {
        return node instanceof UglifyJS.AST_SimpleStatement &&
          node.body instanceof UglifyJS.AST_Assign &&
          node.body.left instanceof UglifyJS.AST_SymbolRef &&
          node.body.left.name === 'y';
      });
      var assignmentStatement = node.body[index].clone();
      node.body.splice(
        index,
        1,
        new UglifyJS.AST_SimpleStatement({
          body: new UglifyJS.AST_Assign({
            left: new UglifyJS.AST_SymbolRef({name: '_x'}),
            operator: '=',
            right: new UglifyJS.AST_SymbolRef({name: 'x'})
          })
        }),
        new UglifyJS.AST_SimpleStatement({
          body: new UglifyJS.AST_Assign({
            left: assignmentStatement.body.left.clone(),
            operator: assignmentStatement.body.operator,
            right: new UglifyJS.AST_SymbolRef({name: '_x'})
          })
        })
      );

      descend(node, this);
      return node;
    }

    node = node.clone();
    descend(node, this);
    return node;
  }));

  var result = transformed.print_to_string({beautify: true});
  return fs.writeFileAsync(path.join(__dirname, 'output.js'), result);
});

这是输出：

var _x;

var x;

var y;

x = 1;

_x = x;

y = _x;

x = 3;

Uglify以AST格式提升变量声明，因此我遵循相同的规则。

在UglifyJS中转换AST

1 个答案: