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peekFromIterator.js
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peekFromIterator.js
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/**
* given an iterator with next() and hasNext() methods,
* create a wrapper iteratior, PeekableInterface which implements
* peek(). peek shows the next element that would be returned on next()
*/
class Iterator {
constructor(iterable = []) {
this.iterable = iterable;
this.index = 0;
}
next() {
const result = this.iterable[this.index];
this.index += 1;
return result;
}
hasNext() {
return this.iterable[this.index + 1] !== undefined;
}
}
// base class tests
{
const iter1 = new Iterator([1, 2, 3]);
console.log(iter1.hasNext());
console.log(iter1.next());
console.log(iter1.hasNext());
console.log(iter1.next());
console.log(iter1.hasNext());
console.log(iter1.next());
console.log(iter1.hasNext());
console.log(iter1.next());
console.log(iter1.hasNext());
}
class PeekableInterface extends Iterator {
constructor(iterable) {
super(iterable);
this.current = super.next();
}
next() {
const prev = this.current;
this.current = super.next();
return prev;
}
peek() {
return this.current;
}
}
{
const peek1 = new PeekableInterface([1, 2, 3]);
console.log(peek1);
console.log(peek1.peek()); // 1
console.log(peek1.hasNext()); // true
console.log(peek1.next()); // 1
console.log(peek1.peek()); // 2
console.log(peek1.peek()); // 2
console.log(peek1.next()); // 2
}