json-key-minify.js

var source = {
	"alpha": "string alpha",
	"bravo": {
		"charlie": "string bravo.charlie",
		"delta": "string bravo.delta",
		"echo": {
			"foxtrot": 'string bravo.echo.foxtrot',
			"gamma": 'string bravo.echo.gamma',
			"hotel": "string bravo.echo.hotel"
		}
	}
},
dictionary = {},
pointer = 'a';

function nextChar(a) {
	return String.fromCharCode(a.charCodeAt() + 1);
}

function getPointer(string) {
	pointer = nextChar(pointer);
	dictionary[pointer] = string;
	return ['@', pointer].join(':');
}

function minifyKeys(obj) {
	var key,
		has = Object.prototype.hasOwnProperty.bind(obj);
	for (key in obj) {
		if (has(key)) {
			switch (typeof obj[key]) {
				case 'object':
					minifyKeys(obj[key]);
					break;
				case 'string':
					obj[key] = getPointer(obj[key]);
			}
		}
	}
}

minifyKeys(source);
setTimeout(function () {
	console.log(source);
	console.log(dictionary);
}, 1000);