How do I create a nested javascript object setting the property names dynamically

Question

I have a javascript callback function which queries my database using a set of parameters. The parameters are set using an object. How can I set the name of one of the properties dynamically?

Right now I have them all just written out. It works fine, it's just a little long. I just need to change the value of two property names. Where propertyNameToChange is in my example code.

var paramToChange = { /* I need to change the name of this property */
    propertyNameToChange: { /* And the name of this property */
      url: { 
        ComparisonOperator: 'EQ',
        AttributeValueList: [{
          S: alreadySetWithVar /* This is already set using a var */
        }]
      }
    },
    TableName: 'ximoRep',
    IndexName: 'url-index'
  }
.... // I have about 10 of these written out. Then my callback function queries using an array using the var name for the object.

var params = [paramOne, paramTwo, paramThree, paramFour, paramFive, paramSix, paramSeven, paramEight];

raduation · Accepted Answer · 2015-08-24 04:54:04Z

2

paramToChange['newPropName'] = paramToChange['propertyNameToChange'];
delete paramToChange['propertyNameToChange'];

Fixed.

answered Aug 24, 2015 at 4:54

raduation

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Comments

jfriend00 · Accepted Answer · 2015-08-24 05:06:35Z

2

Javascript does not have a means of changing the name of a property. What you can do is to assign one property to another new property name and then delete the original property.

If you have this data structure:

var data = {
    prop1: {greeting: "hello"}
};

And, you want to change prop1 to otherProp, you can do it like this:

data.otherProp = data.prop1;
delete data.prop1;

This assigns the value of the original property to a new property and then removes the original property.

The end result is:

var data = {
    otherProp: {greeting: "hello"}
};

A general purpose function for doing this that would even work with propeties that have special characteristics such as getters, setters or other custom attributes would use a propertyDescriptor like this:

function renameProp(obj, oldPropName, newPropName) {
    var descriptor = Object.getOwnPropertyDescriptor(obj, oldPropName);
    Object.defineProperty(obj, newPropName, descriptor);
    delete obj.oldPropName;
}

This assumes the oldPropName property is configurable and the object isn't frozen.

edited Aug 24, 2015 at 5:06

answered Aug 24, 2015 at 4:53

jfriend00

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5 Comments

PitaJ Over a year ago

It's probably best to use propertyDescriptors when possible

jfriend00 Over a year ago

@PitaJ - that extra complication is useful if you think the properties have special attributes. If they're just regular properties, then there's no need.

PitaJ Over a year ago

I was just talking in the general sense. A more general solution would require the use of propertyDescriptors to really cover all of the angles.

jfriend00 Over a year ago

@PitaJ - yeah, I agree. Just not needed for just a bunch of data.

jfriend00 Over a year ago

@PitaJ - I added a function that uses a property descriptor.

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