How can I create a two-way mapping in JavaScript, or some other way to swap out values?

With an extra internal object for reverse mapping. Best if we add a utility class ;) like the following:

ES6 syntax (scroll down for ES5 syntax)

class TwoWayMap {    constructor(map) {       this.map = map;       this.reverseMap = {};       for(const key in map) {          const value = map[key];          this.reverseMap[value] = key;          }    }    get(key) { return this.map[key]; }    revGet(key) { return this.reverseMap[key]; }}

Then you instantiate like this:

const twoWayMap = new TwoWayMap({   '*' : '__asterisk__',     '%' : '__percent__',   ....});

Finally, to use it:

twoWayMap.get('*')   //Returns '__asterisk__'twoWayMap.revGet('__asterisk__')  //Returns '*'

Bonus: If you also need set/unset methods, you can do it (inside the class) easily like:

set(key, value) { this.map[key] = value; }unset(key) { delete this.map[key] }// same for set_reverse and unset_reverse, just use this.reverseMap instead

Equivalent with ES5 (old js) syntax:

function TwoWayMap(map) {   this.map = map;   this.reverseMap = {};   for(var key in map) {      var value = map[key];      this.reverseMap[value] = key;      }}TwoWayMap.prototype.get = function(key){ return this.map[key]; };TwoWayMap.prototype.revGet = function(key){ return this.reverseMap[key]; };

Usage is the same:

var twoWayMap = new TwoWayMap({   '*' : '__asterisk__',     '%' : '__percent__',   ....});twoWayMap.get('*')   //Returns '__asterisk__'twoWayMap.revGet('__asterisk__')  //Returns '*'

Hope this helps. Cheers

Use two objects. One object contains the * -> _asterisk_ mapping, the other object contains _asterisk_ -> *.

var forwardMap = {'*': '__asterisk__', '%': '__percent__', ...};var reverseMap = {};for (var key in forwardMap) {    if (forwardMap.hasOwnProperty(key)) {        reverseMap[forwardMap[key]] = key;    }}

I'd just use a plain object:

var map = { '*': '__asterisk__', '__asterisk__': '*', .... }

If you don't want to have to write all those out, take a look at the implementation of underscore's _.invert(object) here