Use the value of a string variable as the 'index' of an existing object in JavaScript

Question

I am using JavaScript.

I have

var myobj = {
    "one": {
        "name": "paul",
        "no"  : "A123"
    },
    "two": {
        "name": "mike",
        "no"  : "B456"
    },
    "three": {
        "name": "andy",
        "no"  : "C789"
    },
};

I have another object newitem that I want to insert

var newIndex = "four";
var newItem = {
    "name": "leo",
    "no"  : "D987"
};

How do I insert newItem into myobj using newIndex as the 'index'?

By the way, newIndex is not generated by me so I cannot just say myobj.four = newItem; myobj.newIndex = newItem doesn't work since it uses the word 'newIndex' as the index instead of its value.

Any insights?

Christian C. Salvadó · Accepted Answer · 2010-07-20 23:47:17Z

7

Use the bracket notation property accessor:

myobj[newIndex] = newItem;

It is also useful when you want to define a property whose name is not a valid Identifier, e.g.:

obj["1foo"] = "bar"; // `obj.1for` will cause a SyntaxError
obj["a b"] = "bar"; // `obj.a b` will cause a SyntaxError

Note that you can even use an expression with this property accessor, e.g.:

obj[someFunc()] = "foo";

It will evaluate the expression between the brackets, and it will convert the result to string, because JavaScript doesn't have true hash tables, property names must be of type String.

More info:

Member Operators

edited Jul 20, 2010 at 23:47

answered Jul 20, 2010 at 7:07

Christian C. Salvadó

831k185 gold badges929 silver badges845 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Jeff Walden Over a year ago

Note that in the latest edition of the standard on which JavaScript is based, it's not necessary to use bracket notation when referring to properties named by keywords or reserved words: obj.for = 'me' is permitted by ECMAScript 5th edition. (A few other contexts, such as property names in object literals, also have been loosened to permit keywords.) This change has been implemented in Firefox, for one, for a few years now, if you want to play with it.

Christian C. Salvadó Over a year ago

@Jeff, yeah, forgot to mention it, in ES5 an IdentifierName can be used with the . property accessor. I'll make a better example...

Collectives™ on Stack Overflow

Use the value of a string variable as the 'index' of an existing object in JavaScript

1 Answer 1

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related