Is there any way to use a numeric type as an objec

问题:

It seems that when I use a numeric type as a key name in an object, it always gets converted to a string. Is there anyway to actually get it to store as a numeric? The normal typecasting does not seem to work.

Example:

var userId = 1;
console.log( typeof userId ); // number
myObject[userId] = 'a value';
console.dir(myObject);

Dir Output:

{
    '1': 'a value'
}

What I want is this:

{
    1: 'a value'
}

Advice?

Thanks

回答1:

No, this is not possible. The key will always be converted to a string. See Property Accessor docs

Property names must be strings. This means that non-string objects cannot be used as keys in the object. Any non-string object, including a number, is typecasted into a string via the toString method.

> var foo = {}
undefined

> foo[23213] = 'swag'
'swag'

> foo
{ '23213': 'swag' }

> typeof(Object.keys(foo)[0])
'string'

回答2:

In an object, no, but I have found Map extremely useful for this application. Here is where I have used it for numeric keys, a key-based event.

onKeydown(e) {
  const { toggleSidebar, next, previous } = this.props;

  const keyMapping = new Map([
    [ 83, toggleSidebar ],  // user presses the s button
    [ 37, next          ],  // user presses the right arrow
    [ 39, previous      ]   // user presses the left arrow
  ]);

  if (keyMapping.has(e.which)) {
    e.preventDefault();
    keyMapping.get(e.which)();
  }
}

回答3:

Appears to be by design in ECMA-262-5:

The Property Identifier type is used to associate a property name with a Property Descriptor. Values of the Property Identifier type are pairs of the form (name, descriptor), where name is a String and descriptor is a Property Descriptor value.

However, I don't see a definite specification for it in ECMA-262-3. Regardless, I wouldn't attempt to use non-strings as property names.

回答4:

Do we need something like this?

var userId = 1;var myObject ={};
console.log( typeof userId ); // number
myObject[userId] = 'a value';
console.dir(myObject);

Console: Object

1 : "a value"

回答5:

I think you can do the following if you want to use the above thing for accessing it like as a number, I did the same and worked.

var myObj = {"0":"a","1":"b","CNT":2};
$.each(myObj,function(key,value){
     if(isNaN(parseInt(key))){
          return true; //continue;
     }
     //Code to perform operation
}

This works only when the key doesn't start with and numeric character otherwise it'll be converted to a number. See the following example:

parseInt("45kjghk") === 45

I used jQuery here

---

Updated:

var myObj = {"0":"a","1":"b","CNT":2};
$.each(myObj,function(key,value){
     if(isNaN(parseInt(key)) || (key.length !== parseInt(key).toString().length) ){
          return true; //continue;
     }
     //Code to perform operation
}

It may overcome the above problem. Please suggest better if available and problem with this answer if there are.

回答6:

In JavaScript, numerical strings and numbers are interchangeable, so

myObject[1] == myObject['1']

If you really want number to be the key for an object, you might want an array (i.e. created with new Array() or []).