I must reimplement a list and the method forEach with the following instructions:
// Do not construct any array literal ([]) in your solution.
// Do not construct any arrays through new Array in your solution.
// DO not use any of the Array.prototype methods in your solution.
// You may use the destructuring and spreading (...) syntax from Iterable.
the result should look like:
const list = List.create(1, 2)
list.forEach((item) => console.log(item))
Here is my incomplete solution:
export class List {
constuctor(){
}
public static create(...values: number[]): List {
// Do *not* construct any array literal ([]) in your solution.
// Do *not* construct any arrays through new Array in your solution.
// DO *not* use any of the Array.prototype methods in your solution.
// You may use the destructuring and spreading (...) syntax from Iterable.
List list = new List();
values.forEach(function(item){
list.push(item);
});
return list;
}
public forEach(callback: any){
for (let i = 0; i<this.length ; i++){
callback(this[i], i, this);
}
}
}
in the create loop, but the problem, as a static method, the this is not recognized
EDITED thanks to comments
...
thisis not recognised
It is. But you have not given this any property. And this is because:
constuctor should be written as constructorpush method (since you call it in create)length property (since you reference it in forEach)Furthermore, there some other issues:
Array.prototype functions cannot be used, but your code has values.forEach(), ... so that is a violation of that rule. Use a for..of loop instead.Here is your code with those remarks taken on board:
class List {
constructor() {
this.length = 0;
}
push(value) {
this[this.length++] = value;
}
static create(...values) {
let list = new List();
for (let item of values) {
list.push(item);
}
return list;
}
forEach(callback) {
for (let i = 0; i < this.length ; i++) {
callback(this[i], i, this);
}
}
}
const list = List.create(1, 2)
list.forEach((item) => console.log(item))The above "test" will be fine, but when also assignments to properties are to work correctly, like list[2] = 3, then there are more things to take care of. Take for instance this program:
const list = List.create(1, 2);
list[5] = 42; // should update length
list.check = true; // should not update length
console.log("length = " + list.length);
console.log("enumerable keys are " + Object.keys(list));
list.forEach((item) => console.log(item)); // should not output empty slots
list.length = 1; // should delete some index properties
list.forEach((item) => console.log(item)); // should not output deleted items
...then the output should be:
length = 6
enumerable keys are 0,1,5,check
1
2
42
1
You can make this happen by trapping the access to properties, and making length a getter/setter. But you'd also need to distinguish between properties that are array indices, and which are not, so all-in-all that would make the code less trivial.