Dot notation used within a JS function

Jest is one a common testing libraries used in JS. Its syntax uses expect and toBe(val) or notToBe(val) to compare the output of the two values. The following is an example of dot notation, closures (sice its referencing val after execution) and Higher-Order Functions inside a expect function in which we re-implement similar functionality.

This expect function expects a first value. For toBe(val) accepts a second value to compare with. If the two values are equal ===, then it will return true or throw an error "Not Equal" and vice versa for notToBe(val) with !== inequality.

var expect = function(val) {
    return {
        toBe: function(secondVal) {
            if (val === secondVal) {
                return true
            } else {
                throw "Not Equal"
            }
            },
        notToBe: function(secondVal) {
            if (val !== secondVal) {
                return true
            } else {
                throw "Equal"
            }
        }
    }
};

/**
 * expect(5).toBe(5); // true
 * expect(5).notToBe(5); // throws "Equal"
 * expect(5).toBe(null); // throws "Not Equal"
 */