Inject variable into function's scope

Question

Inject variable into function's scope

So, I want to do something like this:

    var a = 'a';

    var dummy = function() {

        // Print out var 'a', from the scope above
        console.log('Dummy a: ' + a);

        // Print out 'b', from the 'compelled' scope
        console.log('Dummy b: ' + b);
    }

    (function() {

        var b = 'otherscope';

        // I know apply won't work, I also don't want to merge scopes
        dummy.apply(this);

        // I want something like this:
        dummy.compel(this, [], {b: 'injected!'});

    })();

But that won't work.

I don't actually want a function to be able to reach 2 scopes, I DO want to be able to set the 'b' variable used inside the dummy function from the outside.

javascript
node.js

Answer 1

You can make b a parameter for the function, or a global variable.

var a = 'a';
var dummy = function(b) {
   ...
}

or

var a = 'a';
var b;
var dummy = function() {
   ...
}

The first allows you to choose when the dummy function has access to the variable, the second allows it to be accessed everywhere.

Answer 2

Use this:

Function.prototype.applyVars = function(Ç$Êscope, Ç$Êparams, Ç$Êscope_variables) {
    if (Ç$Êscope_variables) {
        var Ç$Êvariable, Ç$ÊdefVars = [];
        for (Ç$Êvariable in Ç$Êscope_variables) {
            if (Ç$Êscope_variables.hasOwnProperty(Ç$Êvariable)) {
                Ç$ÊdefVars.push(Ç$Êvariable + '=Ç$Êscope_variables["' + Ç$Êvariable + '"]');
            }
        }
        eval('var ' + Ç$ÊdefVars.join(',') + ';');
        return eval('(' + this + ').apply(Ç$Êscope, Ç$Êparams);');
    }
    return this.apply(Ç$Êscope, Ç$Êparams);
}

// Example

function foo(p1) {
    console.log('Variable [p1]', p1);
    console.log('Variable [x]', x);
    console.log('Variable [y]', y);
}

foo.applyVars(this, ['param X'], { x: "1'2\"3", y: false });

Or this:

function callWithVars(Ç$Êfn, Ç$Êscope, Ç$Êparams, Ç$Êscope_variables) {
    if (Ç$Êscope_variables) {
        var Ç$Êvariable, Ç$ÊdefVars = [];
        for (Ç$Êvariable in Ç$Êscope_variables) {
            if (Ç$Êscope_variables.hasOwnProperty(Ç$Êvariable)) {
                Ç$ÊdefVars.push(Ç$Êvariable + '=Ç$Êscope_variables["' + Ç$Êvariable + '"]');
            }
        }
        eval('var ' + Ç$ÊdefVars.join(',') + ';');
        return eval('(' + Ç$Êfn + ').apply(Ç$Êscope, Ç$Êparams);');
    }
    return Ç$Êfn.apply(Ç$Êscope, Ç$Êparams);
}

// Example

function foo(p1) {
    console.log('Variable [p1]', p1);
    console.log('Variable [x]', x);
    console.log('Variable [y]', y);
}

callWithVars(foo, this, ['param X'], { x: "1'2\"3", y: false });

Answer 3

So, I found a little faster way to do such a thing:

var C = function(ctx, funcBody){
        var newBody = [];

        for(var k in ctx){
            var i =  "var "+k + " = ctx['"+k+"'];";
            newBody.push(i);
        }
        var res = "return function(t){ " +funcBody+ " }";
        newBody.push(res);
        var F = new Function("ctx", newBody.join('\n'));
        return F(ctx);
}
var newFunction = C({"foo":10, "bar":100}, "return foo+bar*t")
newFunction(50);