/* Stack data-structure. It's work is based on the LIFO method (last-IN-first-OUT).
* It means that elements added to the stack are placed on the top and only the
* last element (from the top) can be reached. After we get access to the last
* element, he pops from the stack.
* This is a class-based implementation of a Stack. It provides functions
* 'push' - to add an element, 'pop' - to remove an element from the top.
* Also it implements 'length', 'last' and 'isEmpty' properties and
* static isStack method to check is an object the instance of Stack class.
*/
// Class declaration
class Stack {
constructor() {
this.stack = []
this.top = 0
}
// Adds a value to the end of the Stack
push(newValue) {
this.stack.push(newValue)
this.top += 1
}
// Returns and removes the last element of the Stack
pop() {
if (this.top !== 0) {
this.top -= 1
return this.stack.pop()
}
throw new Error('Stack Underflow')
}
// Returns the number of elements in the Stack
get length() {
return this.top
}
// Returns true if stack is empty, false otherwise
get isEmpty() {
return this.top === 0
}
// Returns the last element without removing it
get last() {
if (this.top !== 0) {
return this.stack[this.stack.length - 1]
}
return null
}
// Checks if an object is the instance os the Stack class
static isStack(el) {
return el instanceof Stack
}
}
export { Stack }