if I have an object, something like this
var o = {
test : 1
}
and I would like to have a second object, one of it's keys should be the value of o.test. Something like this:
var o2 = {
o.test : "bla"
}
I know this is not possible, but is there a better (cleaner) way to do it as I do this now?
Currently what I dow is this:
var o2 = {};
o2[o.test] = "bla"
I guess there is a better way for this?
I guess there is a better way for this?
Assuming I've understood your question correctly then no, not really. The way you've shown is the way to do it. There is no way to use a dynamic key inside the literal itself, so you have to declare it first and then assign the property separately:
var o2 = {};
o2[o.test] = "bla";
o2; // { 1: "bla" }
Update
The full details are given in the spec. Here's the grammar for object literal property identifiers:
PropertyName :
IdentifierName
StringLiteral
NumericLiteral
The StringLiteral production is self-explanatory. Here's what the IdentifierName production does:
The production PropertyName : IdentifierName is evaluated as follows:
- Return the String value containing the same sequence of characters as the IdentifierName.
And for the NumericLiteral production:
The production PropertyName : NumericLiteral is evaluated as follows:
- Let nbr be the result of forming the value of the NumericLiteral.
- Return ToString(nbr).
You can see from this that it is not possible to use anything other than a string inside an object initialiser.
Your Object properties can be any string
var o = {
"whatever you want":1,
"1":"numbers too"
}
o[2]="no numbers, convert to string"
console.log(o["whatever you want"]);//=1
console.log(o["1"]);//=numbers too
console.log(o[new String(2)]);//=no numbers, convert to string
// as James commented, you don't have to convert to string
// I usually do that as to not confuse the object with an array
console.log(o[2]);//=no numbers, convert to string
If all your "property names" are positive integers or 0 you could use an array:
var arr=new Array();//or var arr=[];
var b=22;
arr[10000]="hi";
arr[b]="value";
// normally you would do for(var i=0;len=arr.length;i<len;i++){...arr[i]
// but because there may be many empty spots it's quicker to do:
for(thing in arr){
if(arr.hasOwnProperty(thing)){
console.log(thing + " is " + arr[thing]);
}
}
This being javascript, there is almost always a workaround for doing what you want.
There is no syntax for doing what you want but you can certainly write a function to do it:
function make () {
// Optional sanity check:
if (arguments.length % 2) throw "Number of arguments should be even!";
var obj = {};
for (var name=0,val=1; name < arguments.length; name+=2,val+=2) {
obj[arguments[name]] = arguments[val];
}
return obj;
}
Now you can write this:
var o2 = make(
o.test, 'bla',
'another_key', 'another_val'
);
o2[o.test] == o2[1]