I am trying to solve the exercise "Groups" in Eloquent Javascript (https://eloquentjavascript.net/06_object.html just ctrl+f the word "Groups). To summarize I have to create a class, similar to Set, with four methods: add, delete, has and from. The last one should be static.
This is the solution of the exercise:
class Group {
constructor() {
this.members = [];
}
add(value) {
if (!this.has(value)) {
this.members.push(value);
}
}
delete(value) {
this.members = this.members.filter(v => v !== value);
}
has(value) {
return this.members.includes(value);
}
static from(collection) {
let group = new Group;
for (let value of collection) {
group.add(value);
}
return group;
}
}
let group = Group.from([10, 20]);
console.log(group.has(10));
// → true
console.log(group.has(30));
// → false
group.add(10);
group.delete(10);
console.log(group.has(10));My doubt concern the static method and the way the author chose to iterate the iterable. Why if I change the static method like this:
class Group {
constructor() {
this.members = [];
}
add(value) {
if (!this.has(value)) {
this.members.push(value);
}
}
delete(value) {
this.members = this.members.filter(v => v !== value);
}
has(value) {
return this.members.includes(value);
}
static from(collection) {
let group = new Group;
group = [...collection];
return group;
}
}
let group = Group.from([10, 20]);
console.log(group.has(10));
// → true
console.log(group.has(30));
// → false
group.add(10);
group.delete(10);
console.log(group.has(10));on console.log(group.has(10)); there is the error "group.has is not a function" ?