.softBind() - Rebindable [function].bind() alternative.

BestPractice_Solution.js

// Unless it could become ECMASCRIPT proposal best practice
// would be to use regular function in order to avoid polluting
// [function]'s prototype
// Twitter: https://twitter.com/bitifet/status/1166745132651220992?s=20
const softBind = (function() {
    const master = Symbol();
    return function softBind(self, ...args) {
        const fn0 = self[master] || self;
        const fn = fn0.bind(...args)
        fn[master] = fn0;
        return fn;
    }
})();

function showThis() {
    console.log(this);
};
const a = { name: "a" };
const showA = softBind(showThis, a);
const b = { name: "b" };
const showB = softBind(showA, b);
showA(); // { name: 'a' }
showB(); // { name: 'b' }

Solution_Proposal.js

// Conceptual example of (possible) future .softBind() method
// (Not a good practice thus pollutes function prototype with non standard methods)
// Twitter: https://twitter.com/bitifet/status/1166740427107700736?s=20
(function() {
    const fProto = Object.getPrototypeOf(function(){});
    const master = Symbol();
    fProto.softBind || (
        fProto.softBind = function softBind(...args) {
            const fn0 = this[master] || this;
            const fn = fn0.bind(...args)
            fn[master] = fn0;
            return fn;
        }
    );
})();

function showThis() {
    console.log(this);
};
const a = { name: "a" };
const showA = showThis.softBind(a);
const b = { name: "b" };
const showB = showA.softBind(b);
showA(); // { name: 'a' }
showB(); // { name: 'b' }

The_Problem.js

// Problem example:
// Twitter: https://twitter.com/bitifet/status/1166725486514528259?s=20
function showThis() {
    console.log(this);
};
const a = { name: "a" };
const showA = showThis.bind(a);
const b = { name: "b" };
const showB = showA.bind(b);
showA(); // { name: 'a' }
showB(); // { name: 'a' } // !!!!!!!