evalify.js

const scoped = {
  foo: () => 'foo',
  bar: () => 'bar',
  baz: { a: 'b' },
  arr: [0]
};

const evalify = (code, scope) => {
  const variables = Object.keys(scope)
    .map((name) => {
      const value = scope[name];
      
      if (value.toString() === '[object Object]') {
        return `const ${name} = ${JSON.stringify(value)};`;
      }
      
      if (Array.isArray(value)) {
        return `const ${name} = ${JSON.stringify(value)};`;
      }
      
      return `const ${name} = ${value.toString()};`;
    });
  
  const program = `'use strict';
${variables.join('\n')}

${code}
`;

  return eval(program);
};

const result = evalify('baz.a', scoped);

console.log(result); // 'b'