I had the same need (to test my angularjs app), and the only way I found is to use require.js:

var json = require('./data.json'); //(with path)

note: the file is loaded once, further calls will use the cache.

More on reading files with nodejs: http://docs.nodejitsu.com/articles/file-system/how-to-read-files-in-nodejs

require.js: http://requirejs.org/

The loading of a .json file from a hard disk is an asynchronous operation, and thus it needs to specify a callback function to execute after the file is loaded.

function readTextFile(file, callback) {
    var rawFile = new XMLHttpRequest();
    rawFile.overrideMimeType("application/json");
    rawFile.open("GET", file, true);
    rawFile.onreadystatechange = function() {
        if (rawFile.readyState === 4 && rawFile.status == "200") {
            callback(rawFile.responseText);
        }
    }
    rawFile.send(null);
}

//usage:
readTextFile("/Users/Documents/workspace/test.json", function(text){
    var data = JSON.parse(text);
    console.log(data);
});

This function also works for loading a .html or .txt files, by overriding the mime type parameter to "text/html", "text/plain", etc.