PHP variable property in javascript

Question

In PHP it is common to use variable variables, e.g.

foreach(['key1', 'key2', 'key3'] as $key) {
    if (!$object->$key)
        $object->$key = 'add some values';
}

i wonder how can one do that in javascript?

Practical use case:

we have multiple required input fields (e.g.: name, surname, email) in form with no-validate, values are automatically pushed to this instance (meaning we can access values with this.name, this.surname, etc). We need to ensure these fields are filled.

One could write something like:

if (!this.name)
    this.errors['name'] = 'This field is required.';

if (!this.surname)
    this.errors['surname'] = 'This field is required.';

if (!this.email)
    this.errors['email'] = 'This field is required.';

I am trying to come up with something more compact and accurate like:

['name', 'surname', 'email'].forEach(function (field) {
    if (!this.[field])
        this.errors[field] = 'This field is required.';
});

Possible duplicate of Dynamically access object property using variable — VLAZ
– VLAZ, Commented Sep 18, 2019 at 14:45
What is this in your JS example? i.e. is it an array, an object, or something else? — Martin
– Martin, Commented Sep 18, 2019 at 14:45
this.[field] -> this[field] although you also need to make sure the correct context is preserved — VLAZ
– VLAZ, Commented Sep 18, 2019 at 14:45
Also, those aren't variable variables - in PHP a variable variable is $key = "dynamic"; $$key = "dynamically set"; where $$key would resolve to the variable $dynamic — VLAZ
– VLAZ, Commented Sep 18, 2019 at 14:48
@Taplar variable variables are a thing in PHP. Look at my other comment. Basically, you use the value of one variable to access another by name. It's...very unwieldy. — VLAZ
– VLAZ, Commented Sep 18, 2019 at 14:49

Mischa · Accepted Answer · 2019-09-18 14:57:30Z

1

U can do that almost same way as in php:

class Person {

  constructor(name, surname, email) {
    this.name = name;
    this.surname = surname;
    this.email = email;
    this.errors = {}
  }
  
  validate () {
    ['name', 'surname', 'email'].forEach((field) => {
      if (!this[field])
          this.errors[field] = field + ' is required.';
    });
  }
  
  getErrors() {
    return this.errors;
  }
}

let s = new Person('john','doe');
s.validate();
console.log(s.getErrors());

answered Sep 18, 2019 at 14:57

Mischa

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