Capture caller's scope in JavaScript

Question

Capture caller's scope in JavaScript

This code works as a is in the same scope where eval runs:

function compile(fn) {
    //Actually calls fn.toString() then compiles some es.next type 
    //features to current versions of es.
    return 'function () { return a; }';
}

function runAsStringA() {
    var a = 10;
    var compiled = eval(compile());
    return compiled();
}

This doesn't work, but matches what I'd like to do in an ideal world:

function compile(fn) {
    return eval('function () { return a; }');
}

function runAsStringA() {
    var a = 10;
    var compiled = compile();
    return compiled();
}

Essentially I need a way to eval in the parent's scope.

I tried:

function compile(fn) {
    return eval.bind(this, 'function () { return a; }');
}

function runAsStringA() {
    var a = 10;
    var compiled = compileSpecialFunction()();
    return compiled();
}

The problem is that then the compiled function doesn't get a in scope.

I'm attempting to use this in a node.js environment, so it's fine if a solution only works on node.js

It can even require some native code, although I have no experience writing native add-ons.

javascript
node.js
eval

Answer 1

Unfortunately this seems to be impossible.

Answer 2

While I agree that you should avoid eval, and probably veal (as my spell checker suggests), this might help:

function compile(a) {
    return eval('(function(a) { return a; })').call(this, a);;
}

function runAsStringA() {
    var a = 10;
    var compiled = compile(a);
    return compiled;
}

console.log(runAsStringA());