check if an object has same field's value ​​as defined in an array

Question

I have an array like this:

var Items = new Array({ name: "aaa", field: "bbb", val: true },
                      { name: "ccc", field: "ddd", val: false })

I want to check if a certain object has same field's value ​​as defined in the field & val of the array.

I did this:

var obj = {bbb: false, ddd: false} #(I'm getting the obj from API, but this is what I have when I print obj to log)

_.each(Items, function(item){
   if (obj[item.field] === item.val)  
     console.log(obj[item.field],"=",item.val);
});

But I got undefind=undefined .

When I tried obj['bbb'] OR obj[String(item.field)] , I got the value.

Also, see following logs inside the loop:

console.log(typeof item.field, typeof "bbb");
=> string string
console.log(obj["bbb"], obj[item.field], obj[String(item.field)], item.field);
=> false undefined false "bbb" 

Does Anybody know why this happens?

Answer 1

To compare objects, it's simpler to just use _.isEqual (see http://underscorejs.org/#isEqual ). Javascript has some very wierd quirks, for example http://www.sitepoint.com/javascript-truthy-falsy/

Answer 2

An objects property name must be a string , any string is valid including an empty string (the truth is the same is really true of arrays, except that the numbers get converted to a string (for example Items[0] is really Items["0"] )).

When you are comparing to obj[item.val] you are (for the sample array you provided) checking for a property name that is a boolean which isn't valid. When you instead use obj[String(item.val)] you are first converting the value true or false to a string so it becomes "true" or "false" .

Here's a link to a jsfiddle