What would be the best way to remove any additional properties from an object that is not defined in defaults object?

var
defaults = { color : 'blue', size: 9, price : 40.00, instock : true
},
newItem = { color: 'red', size : 4, price : 20.00 extra : invalid // discard this extra1 : invalid // discard this
},
item = $.extend( defaults, newObject ) ;

Desired output....

{ color : 'red', size: 4, price : 20.00, instock : true
}

2

5 Answers

According to this performance comparison:

The most efficient way to do this is:

for(attr in newItem) { if(defaults[attr] === undefined) delete newItem[attr];
}

Before you call $.extend, put the following.

for(variable in newItem) { if(!(variable in defaults)) { delete newItem[variable]; }
}

This will loop over every key in newItem and check that it is also a key in defaults. Note that this will modify newItem, so if that is not desired, you'll need to do some tweaking.

You could reduce Object.keys(defaults) to an object containing either the override value or the default value:

var defaults = { color : 'blue', size: 9, price : 40.00, instock : true
},
newItem = { color: 'red', size : 4, price : 20.00, extra : 'invalid', extra1 : 'invalid'
};
function getOverrides(defaults, obj) { return Object.keys(defaults).reduce(function(result, cur) { result[cur] = cur in obj ? obj[cur] : defaults[cur]; return result; }, {});
}
console.log(getOverrides(defaults, newItem));

Only merge properties which existing in defaults object: (simple and supports old browsers)

var defaults = { color : 'blue', size: 9, price : 40.00, instock : true
};
var newItem = { color: 'red', size : 4, price : 20.00, extra : 'invalid', // discard this extra1 : 'invalid' // discard this
};
var result = {};
for (var i in defaults) { result[i] = newItem.hasOwnProperty(i) ? newItem[i] : defaults[i];
}
console.log(result);

Some code that I have been playing with that may be of interest, and an example of how to use it with your question.

'use strict';
var slice = Function.call.bind(Array.prototype.slice);
var reflectAssign = function assign(target) { return slice(arguments, 1).every(function(source) { if (source == null) { return true; } var object = Object(source); return Reflect.ownKeys(object).every(function(key) { return Reflect.set(target, key, object[key]); }); });
};
var reflectAssignHas = function(target) { var targetKeys = Reflect.ownKeys(target); return slice(arguments, 1).every(function(source) { if (source == null) { return true; } var object = Object(source); return targetKeys.every(function(key) { return Reflect.has(object, key) ? Reflect.set(target, key, object[key]) : true }); });
};
var defaults = { color: 'blue', size: 9, price: 40.00, instock: true
};
var newItem = { color: 'red', size: 4, price: 20.00, extra: 'invalid', // discard this extra1: 'invalid' // discard this
};
var item = {};
console.log(reflectAssign(item, defaults));
console.log(reflectAssignHas(item, newItem));
console.log(item);

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