calling eval() in particular context

Question

I have following javaScript \"class\":

A = (function() {
   a = function() { eval(...) };
   A.prototype.b = function(arg1, arg2) { /* do something... */};
}         


        

Answer 1

I was struggling with this for a while in Angular, and found this answer the most useful. I was trying to implement some existing code which use 'with', not allowed by strict. My 'knife and fork' solution to not having to use 'this.' inside the expression I wanted to evaluate, and avoiding 'with' and 'eval' was:

let evalInContext = function (js, context) {
    let keys = Object.keys(context);
    //let code = 'function it(){';
    let code = '';
    for (let i = 0; i < keys.length; i++){
        code += 'let '+keys[i]+' = window._evalincontextobj.'+keys[i]+';\n';
    }
    code += 'return (';
    code += js;
    code += ')';//}\n return it();';
    window['_evalincontextobj'] = context;
    let res = Function(code)();
    console.log(js+' = '+res);
    delete window['_evalincontextobj'];
    return res;
}

This is working for expressions like (watched === 'hello') where 'watched' is a member of context.