Object.defineproperty Or .prototype?

I've seen two different techniques of implementing non-native features in javascript, First is: if (!String.prototype.startsWith) { Object.defineProperty(String.prototype, 'sta

Solution 1:

In two cases you are adding a new property 'startsWith' in String.prototype.

First differs from the second in this cases:

You can configure the property to be enumerable, writable and configurable.

Writable - true means that you can change its value by assigning any value. If false - you can't change the value

Object.defineProperty(String.prototype, 'startsWith', {
        enumerable: false,
        configurable: false,
        writable: false, // Set to Falsevalue: function(searchString, position) {
            position = position || 0;
            returnthis.lastIndexOf(searchString, position) === position;
        }
    });

var test = newString('Test');

test.startsWith = 'New Value';
console.log(test.startsWith); // It still have the previous value in non strict mode

Enumerable - true means that it will be seen in the for in loop.

Object.defineProperty(String.prototype, 'startsWith', {
        enumerable: true, // Set to Trueconfigurable: false,
        writable: false, 
        value: function(searchString, position) {
            position = position || 0;
            returnthis.lastIndexOf(searchString, position) === position;
        }
    });

var test = newString('Test');

for(var key in test){
   console.log(key)  ;
}

Configurable - true if and only if the type of this property descriptor may be changed and if the property may be deleted from the corresponding object.

Object.defineProperty(String.prototype, 'startsWith', {
            enumerable: false,
            configurable: false, // Set to Falsewritable: false, 
            value: function(searchString, position) {
                position = position || 0;
                returnthis.lastIndexOf(searchString, position) === position;
            }
        });

    
    deleteString.prototype.startsWith; // It will not delete the propertyconsole.log(String.prototype.startsWith);

And one advice to you, don't change the prototypes of build in types.