How to call this inside for example forEach in class?

Question

I lean Node.js and JavaScript. I have example class:

class Student {
    constructor(name, age) {
        this.name = name;
        this.age = age;
    }
    getStudentName() {
        return this.name;
    }
    getStudentAge() {
        return this.age;
    }
    exampleFunction() {
        let array = ['aaa', 'bbb', 'ccc', 'ddd'];
        array.forEach(function(i, val) {
            console.log(i, val);
            console.log(this.getStudentName()); // ERROR!
        })
    }
}

var student = new Student("Joe", 20, 1);
console.log(student.getStudentName());
student.exampleFunction();

How can I refer to a method from a function inside a forEach in this class?

I have TypeError:

TypeError: Cannot read property 'getStudentName' of undefined

fat arrow function FTW! `array.forEach((i, val) => {` – epascarello Jul 18 '17 at 19:37 — epascarello, Jul 18 '17 at 19:37

Nikhil Vartak · Answer 1 · 2017-07-18T19:44:54.020

7

You need to pass this reference in forEach.

array.forEach(function(i, val) {
   console.log(i, val);
   console.log(this.getStudentName()); // Now Works!
}, this);

edited Jul 18 '17 at 19:44

answered Jul 18 '17 at 19:38

Nikhil Vartak

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score 4 · Accepted Answer · answered Jul 18 '17 at 19:39

'this' changes inside that for loop. You have to force the definition of it. There are several ways to do it. Here is one

   class Student {
    constructor(name, age) {
        this.name = name;
        this.age = age;

    }
    getStudentName() {
        return this.name;
    }
    getStudentAge() {
        return this.age;
    }
    exampleFunction() {
        let array = ['aaa', 'bbb', 'ccc', 'ddd'];
        array.forEach(function(i, val) {
            console.log(i, val);
            console.log(this.getStudentName()); // ERROR!
        }.bind(this))
    }
}

How to call this inside for example forEach in class?

2 Answers2