I have a class to which I would like to include a method of overriding some of the default instance variables in the constructor, without having a dozen parameters. I would like to do this by passing an object in the form of:
class MyClass {
constructor(overrides) {
this.instanceVar1 = default1;
this.instanceVar2 = default2,
for (key in overrides) {
this.key = overrides[key];
}
}
let overrides = {instanceVar1 : value,
instanceVar2 : value2};
let instance = new MyClass(overrides);
console.log(instance.instanceVar1) // Outputs value, not default1.
In Python this could be done with
if overrides is not None:
for key, value in overrides.items():
self.setattr(self, key, value)
Is there a JS equivalent or do I just have to add a bunch of parameters with default values?
For your given example you simply need to use bracket notation to access a property from a variable.
class MyClass {
constructor(overrides) {
this.instanceVar1 = 'default1';
this.instanceVar2 = 'default2';
for (const key in overrides) {
this[key] = overrides[key];
// ^^^
}
}
}
let overrides = {
instanceVar1: 'value',
instanceVar2: 'value2'
}
let instance = new MyClass(overrides);
console.log(instance.instanceVar1); // valueAn alternative would be to destructure the needed parameters from the overrides object setting appropriate defaults, and leaving the ...rest for use elsewhere.
class MyClass {
constructor({
instanceVar1 = 'default1',
instanceVar2 = 'default2',
...overrides
}) {
this.instanceVar1 = instanceVar1;
this.instanceVar2 = instanceVar2;
console.log(overrides); // { extraVar1: 'another value' }
}
}
let overrides = {
instanceVar1: 'value',
instanceVar2: 'value2',
extraVar1: 'another value'
}
let instance = new MyClass(overrides);
console.log(instance.instanceVar1); // value