Question

I’m confused about the different ways to declare functions inside a constructor function.

function ClassName() {
 this.one = function() {};
 var two = function() {};  
 three = function() {};
}

I know one is public and can be called by the outside and two is private. What are the semantics for three?

Answer 1

The example as you have provided would be a syntax error, as you need to use = for assignment in that context.

three if used with the correct assignment operator would be a global function that would exist outside of that scope. When you omit the var keyword, the variable is assigned a property of the global object, which is window in a browser.

jsFiddle.

When using var, they become properties of the VariableObject in the execution context. You use them as normal variables.

Further Reading.