Global scroll restoration flag

scroll-restoration-global-flag.js

/* jshint esnext: true */

// A simple experimental poly-fill to create a global flag that controls scroll restoration.
// To use simply set window.history.scrollRestoration to 'manual' or 'auto'.
// Requires Chrome v44 with "--enable-web-experimental-features" flag.
(function(window, console, undefined) {
  "use strict";
  var history = window.history;

  // History API does not support scroll restoration option
  if (!('options' in history && 'scrollRestoration' in history.options)) {
    console.log('Warning: scrollRestoration option is not available.');
    return;
  }

  // Exit early if this poly-fill has already been executed
  if (history.scrollRestoration) {
    console.log('Warning: history.scrollRestoration is already defined.');
    return;
  }

  // create global flag and ensure its changes are reflected to the per-state option
  Object.defineProperty(history, 'scrollRestoration', {
    set: function(v) {
      if (v !== 'auto' && v !== 'manual')
        throw 'scrollRestoration can only be {auto|manual}.';

      var changed = v !== this.scrollRestoration;
      if (changed) {
        // update current state to reflect the new scroll restoration option
        history.replaceState(history.state, '', undefined, {'scrollRestoration': v});
        console.assert(history.options.scrollRestoration == v);
      }
    },
    get: function() {
      return history.options.scrollRestoration;  
    }
  });

  // Curry {push, replace}State functions to pass the global flag
  for (var property of ['pushState', 'replaceState']) {
    Object.defineProperty(History.prototype, property, {
      value: curry(History.prototype[property])
    });
  }
  
  function curry(fn) {
    if (!fn) {
      console.warn("Warning: can't curry " + fn);
      return fn;
    }
    
    return function() {
      var options = {'scrollRestoration': history.scrollRestoration};
      var args = Array.prototype.slice.call(arguments);
      switch(args.length) {
        // first two arguments are required.If not provided we will let fn throw.
        case 2: args.push(undefined);
        case 3: args.push(options);
        case 4: /* no-op: allow user to override global flag */
      }
      fn.apply(this, args);
    };
  }

}(window, console));