Min stack [https://leetcode.com/problems/min-stack]

min_stack.js

var MinStack = function() {
    this.stack = []
    this.historyStack = [];
};

/** 
 * @param {number} val
 * @return {void}
 */
MinStack.prototype.push = function(val) {
    this.stack.push(val);

    const currentLocalMin = this.getMin();
    const historyMin = val !== undefined && currentLocalMin > val || currentLocalMin === undefined 
        ? val 
        : currentLocalMin;

    this.historyStack.push(historyMin);
};

/**
 * @return {void}
 */
MinStack.prototype.pop = function() {
    this.stack.pop();
    this.historyStack.pop();
};

/**
 * @return {number}
 */
MinStack.prototype.top = function() {
    return this.stack[this.stack.length - 1];
};

/**
 * @return {number}
 */
MinStack.prototype.getMin = function() {
    return this.historyStack[this.historyStack.length - 1];
};