Internal

Subjects

var a = 10;
console.log(a);

var workersUp = function(targetCnt) {
    return Cluster.workers().length == targetCnt;
};

A JavaScript identifier must start with lower or upper case letter, underscore (_) or dollar ($). Subsequent characters may include digits.

The Underscore identifier: it is frequently used to preface the name of an object's property or method that is private.

_.range(1, 100000): a function to create flexibly numbered lists of integers: https://underscorejs.org/#range

_.map(list, iteratee, [context]): https://underscorejs.org/#map

Arrow function expression () =>. The arrow function expression is a syntactically compact alternative to a regular function expression https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/Arrow_functions. The basic syntax:

(param1, param2, …, paramN) => { statements }

(param1, param2, …, paramN) => expression
// equivalent with:
 => { return expression; }

When there is one parameter parentheses are optional:

(param) => { statements }
// equivalent with:
param => { statements }