accessing javascript object from function

Question

Why does first work and not the latter?? *its only a minor difference where in the latter case i used the shorthand for accessing cats object property. I read that it shouldn't make any difference if "name of the property would be a valid variable name ― when it doesn't have any spaces or symbols in it and does not start with a digit character."

    //this works 
    var cats = {Spot:true};

    function addCat (name) {   cats[name] = true; }

    addCat("white");

    console.log ("white" in cats);  //true

    console.log (cats.white); //true

    //this doesn't work 
    var cats = {Spot:true};

    function addCat (name) {   cats.name = true; }

    addCat("white");

    console.log ("white" in cats); //false

    console.log (cats.white); //undefined

Also duplicate of [Difference between using bracket (`[]`) and dot (`.`) notation](http://stackoverflow.com/q/17189642/218196) — Felix Kling, Jul 18 '13 at 19:08

score 5 · Accepted Answer · answered Jul 18 '13 at 19:02

In your second code, cats.name is not dynamic so your not getting the value of name in the function; however, you are setting a property called name:

//this works
var cats = {
    Spot: true
};

function addCat (name) {   
    cats.name = true; 
    // use cats[name] like in your first example
}
addCat("white");

console.log(cats); 
/*
{
    Spot: true,
    name: true
}
*/

console.log ("name" in cats); //true
console.log (cats.name); // true

accessing javascript object from function

1 Answers1