Bind functions to instances in a way that maintains strict equality when done multiple times

bind-once.js

const bindings = new WeakMap()

const getFns = context => {
  if (!bindings.has(context)) {
    bindings.set(context, {})
  }
  return bindings.get(context)
}

const bindOnce = (fn, context, ...args) => {
  const fns = getFns(context)
  const key = fn.toString()
  if (!fns[key]) {
    fns[key] = [];
  }
  const sameArg = (arg, index) => arg == args[index];
  const withArgs = fns[key].find(fnInfo => fnInfo.args && fnInfo.args.every(sameArg));
  return withArgs ? withArgs.fn : fns[key].push({
    fn: fn.bind(context, ...args),
    args
  }).fn;
}

export default bindOnce