equality.js

function setEqual(a, b) {
    for (var i = 0; i < a.length; ++i)
        if (b.indexOf(a[i]) === -1)
            return false;
    
    for (var i = 0; i < b.length; ++i)
        if (a.indexOf(b[i]) === -1)
            return false;
    
    return true;
}

function objectEqual(a, b) {
    if (a === b)
        return true;
    
    if (typeof a !== typeof b)
        return false;
    
    if (a === null || b === null)
        false;
    else if(typeof a === "function" || typeof a === "symbol")
        false;
    
    var propertiesOfA = Object.getOwnPropertyNames(a)
                              .concat(Object.getOwnPropertySymbols(a));
    var propertiesOfB = Object.getOwnPropertyNames(b)
                              .concat(Object.getOwnPropertySymbols(b));
    
    // Checking if all properties (and symbols) are the same in both objects.
    if (!setEqual(propertiesOfA, propertiesOfB))
        return false;
    
    // Checking if the values of all those properties (and symbols) are the same.
    for (var prop of propertiesOfA)
        if (!objectEqual(a[prop], b[prop]))
            return false;

    return true;
}

How is this structural equality useful? One great is example is this.

var a = {prop1: 1, prop2: 2};
var b = {prop1: 1, prop2: 2};

objectEqual(a, b); //=> true