Running JS code in a limited context

Question

I am trying to run trusted JS code in an isolated context. This method was mainly developed:

function limitedEval(src, context) {
    return (function() {
        with(this) {
            return eval(src) 
        }
    }).call(context)
}

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This works fine, however, when the script uses the keyword var, it is stored in the execution context, and not in the provided context in the with statement (which I understand by design). So, for example, the following code does not work:

var ctx = {};
limitedEval('var foo = "hello"', ctx);
limitedEval('alert(foo)', ctx); // error: foo is undefined

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I would like to be able to call limitedEval () several times and reuse the context. Is it possible?

Answer 1

. , limitedEval. , , var, . 1 . - generators. - , , .

// IIFE to store gen_name
var limitedEval = function() {
    // Symbol for generator property so we don't pollute `ctx` namespace
    var gen_name = Symbol();

    return function limitedEval(src, context) {
        if(!(gen_name in context)) {
            // Generator that will run eval and pause til getting the next source code
            var generator = function * () {
                with(this) {
                    while(true) {
                        yield eval( yield );
                    }
                }
            };

            context[gen_name] = generator.call(context);

            // Initially, we need to execute code until reaching the first `yield`
            context[gen_name].next();
        }

        // First, send the source to the `eval`
        context[gen_name].next( src );

        // Second, get the `eval` result
        return context[gen_name].next().value;
    };
}();

var ctx = {};
limitedEval('var foo = "hello"', ctx);
limitedEval('alert(foo);', ctx);

limitedEval , ctx. , ctx. ctx, var. . ctx, .

, .

: , Symbol with(this) with(context)