I am looking to create a custom method in JavaScript that allows me to access a property of the preceding method or function. For example:
//default
var arr = [1,6,3,5];
alert(arr.length);
Instead of using the standard length method, I want to implement my own custom method called len. Example:
//custom
prototype.len = () => {
return prototype.length;
}
var arr = [1,6,3,5];
alert(arr.len);
If you want to create a "getter" without using ES6 class syntax, you can achieve this by utilizing the Object.defineProperty method:
Object.defineProperty(Array.prototype, 'size', {
get: function() {
return this.length;
}
});
When you use .defineProperty, it will automatically produce a property that is not enumerable, ensuring that your new property won't show up unexpectedly in a for .. in ... loop.
There are differing opinions on whether adding such properties to built-in classes is advisable, with some programming languages endorsing it while others do not.
If you want to define your own method for prototype, there are a few different approaches you can take:
// You could use Object.defineProperty as well
Array.prototype.len = function() {
return this.length // --> this will be an array
}
After defining the method, you can call it like this:
[1, 2, 3].len()
However,
It's generally considered bad practice to add new functions to built-in prototypes because it can lead to issues such as accidentally redefining existing methods or conflicting with future updates. A better approach would be to create your own prototype and use that instead.
function MyArray () {
// Your code here
}
MyArray.prototype = Object.create(Array.prototype) // Inheritance
MyArray.prototype.len = function () {
return this.length
}
Alternatively, you could simply create a standalone function and pass the array as an argument or use it as this:
Passing the array as an argument:
function len (array) {
return array.len
}
Using this:
function len() {
return this.len
}
// Invoking the function
len.call(array)
If you want to achieve this, you can follow these steps:
Define a new method called len using the Array prototype:
Array.prototype.len = function () {
return this.length;
};
However, it's worth considering other options as well. You may find more efficient solutions in the comments section below.
If you want to customize existing objects by adding your own methods or properties, such as the built-in Array object in the example you provided, you must be specific in your approach. For example:
Array.prototype.size = function() { return this.length; };
[4, 5, 6].size(); // this will give you the result of 3
Remember that when using this, it refers to the array on which the method is called. Using an ES6 arrow function may affect the scope and therefore alter the value of this.
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