Use variable value as variable name in function

Question

In the code below:

DbModels.prototype.updateById = function(_collection, id, field, value, callback) {
    this.getCollection(_collection, function(error, sel_collection) {
      if( error ) callback(error)
      else {
        sel_collection.update({_id: ObjectID.createFromHexString(id)}, {$set: {$[field].value:value}}, function(error, updated) {
          if( error ) callback(error)
          else callback(null, updated);
        });
      }
    });
};

I would like to use the value of the variable field as the name of the variable in $set. I tried using the following code $[field].value (as you can see in the code above), which doesn't work. Any suggestions how to solve this?

Thanks!

The answer is simple: Do not create messy code where hacks like dynamic variable names are necessary. — ThiefMaster
– ThiefMaster, Commented Mar 23, 2012 at 8:10
What exactly is messy about this approach? What I intend to do is pass the attribute that needs to be updated and then (dynamically) update only the changed attribute. — The Code Buccaneer
– The Code Buccaneer, Commented Mar 23, 2012 at 8:19

kirilloid · Accepted Answer · 2012-03-23 08:06:01Z

6

There's not such syntax in javascript as php ${$var_name};

One can use this[var_name] or window[var_name] (for global vars in browsers), but there's no way to get local variable in current scope except eval, which is definitely considered bad.

Consider using a hash (object) for variable "scoping/namespacing".

answered Mar 23, 2012 at 8:06

kirilloid

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2 Comments

The Code Buccaneer Over a year ago

With the last part do you mean something like: var parameters = {}; parameters[firstVariableName] = field; sel_collection.update({_id: ObjectID.createFromHexString(id)}, {$set: {parameters[firstVariableName]:value}},................

kirilloid Over a year ago

Yes, except one can't write object literals this way. And it could be actually done a bit simpler:

var setParameters = {}; setParameters[parameters[firstVariableName]] = value; sel_collection.update({_id: ObjectID.createFromHexString(id)}, {$set: setParameters}

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