Given Code
var isEmptyArray = function (array) {
if (typeof array !== 'undefined' && array.length > 0) {
}
Usage
isEmptyArray(myArray);
Wanted Result
How can I re-write above to be able to use:
myArray.isEmptyArray();
Add a comment
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1 Answer
Just javascript:
Array.prototype.isEmptyArray = function() {
return this.length === 0;
}
Typescript:
interface Array<T> {
isEmptyArray(): boolean;
}
Array.prototype.isEmptyArray = function() {
return this.length === 0;
}
Edit
The above solution will work for all instances of Array, for example:
let a = [];
console.log(a.isEmptyArray()); // true
a.push(1);
console.log(a.isEmptyArray()); // false
You can create your own array class and then implement needed methods just there (without affecting other Array instances):
class MyArray<T> extends Array<T> {
public isEmptyArray(): boolean {
return this.length === 0;
}
}
let a1 = [];
console.log(a1.isEmptyArray()); // Uncaught TypeError: a.isEmptyArray is not a function
let a2 = new MyArray<any>();
console.log(a2.isEmptyArray()); // true
This approach is good when you're using other js libraries which are not aware of the changes you've made in the Array prototype.
7 Comments
Nitzan Tomer
It has nothing to do with Angular, it's just a matter of having the method in all array instances or just specific ones. I updated my answer.
linguamachina
This approach is bad because you're augmenting
Array's prototype with a completely trivial operation. Surely it's more performant and equally readable to simply inline if(arr.length === 0)? If you aren't sure if arr exists, simply use if(arr && arr.length)...Nitzan Tomer
@headeronly In Object Oriented, the point is to have the ability to add methods to your classes. If you check a lot whether or not an array is empty then it makes much sense to put that into a method
linguamachina
@NitzanTomer This is not an OO vs. functional programming issue. Mutating the prototype of built-in objects has a bad smell about it. You are modifying a standardised, well-documented API for the sake of adding a trivial helper function. It's not "your" class. See stackoverflow.com/questions/14034180/…
Nitzan Tomer
@headeronly It depends on the scenario. And I wrote that in my answer, if there are no scripts in your page that might get broken because of that then there's no reason why not.
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