Accessing variables indirectly [duplicate]

问题:

This question already has answers here:

Dynamically access object property using variable (14 answers)

Closed 5 years ago.

Within my code (javascript in a firefox extension), i have a list of some variables, like this:

var myApp = {
 var1: true,
 var2: false,
 var3: true,
 var4: false
};

I want to access these variables to get their value indirectly using a function:

var myApp = {
 var1: true,
 var2: false,
 var3: true,
 var4: false,

 varGetter: function(aName) {
  // code
  return myApp.aName.value;
 }
};

I call this function like this for example:

if(myApp.varGetter("var2")) {alert("true")};

Now, how this function can be implemented to do what i want?

回答1:

The problem is that you are trying to access a property with the dot notation and the variable.

myApp.aName.value;

this sometimes creates new property or returns undefined

You should use this notation instead

myApp[aName];

回答2:

You can use myApp[aName] to use a variable as a property name:

var myApp = {
 var1: true,
 var2: false,
 var3: true,
 var4: false,

 varGetter: function(aName) {
  return myApp[aName];
 }
};

console.log(myApp.varGetter("var1")); // true

Also, to avoid hardcoding myApp in your function you can replace it with this[aName].

回答3:

You can access gloval variables via the window variable. Example:

var foo = 'asdf';
alert(window['foo']);

To get json variables, use the same notation:

var myApp = {
 var1: true,
 var2: false,
 var3: true,
 var4: false
};

function varGetter(name) {
    return myApp[name];
}

EDIT: Misread the question.

回答4:

If what you want to do is encapsulation (keeping variables private), you should use the module pattern, which would give you that :

var myApp = (function(){
    //you can't access those variable doing myApp.var1 for example
    var data = {};
    data.var1 = true;
    data.var2 = false;
    data.var3 = true;
    data.var4 = false;

    //then explicitly make your getter/setter
    function varGetter(varName){
        return data[varName];
    }

    //finally, return an object into myApp, out of this closure
    return {
        varGetter : varGetter
    };
})()