Javascript 'this' value changing, but can't figure out why

Question

I\'m a total Javascript newb, and I\'m trying to wrap my head around OLN. What I\'m encountering is that, when calling an object method from another method on the same objec

Answer 1

First of all, I would encourage you to avoid eval where you don't need it, for example, in your fist function:

//...
generateForLevelSkillAndCount : function(level, skill, count) {
    var functionCall = this['generate_' + level + '_' + skill];
    return functionCall(count);
},
//...

You can use the bracket notation property accessor instead eval, it's unnecessary in this case.

Now, I guess you are trying your code on the Chrome's Console, and eval is failing because the console has a bug, when eval is invoked from a FunctionExpression (such as generateForLevelSkillAndCount), the evaluated code uses the Global context for its Variable Environment and Lexical Environment.

See this answer for more information on this bug.

Edit: After re-reading your code, the problem happens because you lose the base object reference when you assign the function to your functionCall variable, you can either:

Invoke the function directly, without using that variable:

//...
generateForLevelSkillAndCount : function(level, skill, count) {
    this['generate_' + level + '_' + skill](count);
},
//...

Or still use your variable, but persist the this value:

//...
generateForLevelSkillAndCount : function(level, skill, count) {
    var functionCall = this['generate_' + level + '_' + skill];
    return functionCall.call(this, count);
},
//...

More info on this...