forEach not working for the array inside an object in javascript

Asked Apr 28 '20 at 18:27

Active Apr 28 '20 at 18:31

Viewed 133 times

I'm new to javascript, so when I was trying to iterate an array which is an attribute of an object, using a method of the same object, It is showing error. This is the code:

let obje = {
    data : [1,2,3,4],
    print :  ()=> {
        this.data.forEach(element => {
            console.log(element);
        });
    }
}

obje.print()

This is the error i get:

Uncaught TypeError: Cannot read property 'forEach' of undefined
    at Object.print (script.js:13)
    at script.js:19

But when i do this same thing without arrow function, it works

let obje = {
    data : [1,2,3,4],
    print :  function() {
        this.data.forEach(element => {
            console.log(element);
        });
    }
}

obje.print()

Output:- 
1
2
3
4

asked Apr 28 '20 at 18:27

TheGunSlinger

3

Don't use arrow function as a method in an object literal. – Teemu Apr 28 '20 at 18:29
thats because, arrow function have **lexical this** and which is not the `this` you expect it, probably `global` – Mhmdrz_A Apr 28 '20 at 18:30
`this` is undefined inside your arrow function. See https://stackoverflow.com/questions/38589227/why-this-is-undefined-inside-a-fat-arrow-function-definition. – Zoldszemesostoros Apr 28 '20 at 18:31
Can you read up on this in ES6. Your issue is related to the scope of this in both functions. Read more on this via this link https://medium.com/@thatisuday/understanding-this-in-es5-vs-es6-579caa749bce – Balanced02 Apr 28 '20 at 18:32
thanks man, but i want to know that, is it a bad practice to use arrow function in an object literal – TheGunSlinger Apr 28 '20 at 18:32
1

@Zoldszemesostoros it's `window`, not `undefined`, or the error would be `Cannot read property 'data' of undefined` – Patrick Roberts Apr 28 '20 at 18:32
@PatrickRoberts yes, you have right, it's late here... – Zoldszemesostoros Apr 28 '20 at 18:34
@RhythemParashar No, it's not bad practice, but if you're using `this` in an arrow function, you've to know what you're doing. – Teemu Apr 28 '20 at 18:36
thanks for your responce guys :) – TheGunSlinger Apr 28 '20 at 18:37
@Teemu ok man, gotcha – TheGunSlinger Apr 28 '20 at 18:41

forEach not working for the array inside an object in javascript

0 Answers0