osmium.js

var osmium = require('osmium');
    levelup = require('levelup');

var db = levelup('./' + (process.argv[3] || 'test.ldb'));
var count = 0;
var batch = [];
var batchSize = 100000;

var reader = new osmium.Reader(process.argv[2], {
    'node': true,
    'way': true
});

function nextBuffer() {
    var buffer = reader.read();
    if (!buffer) return pushBatch(batch);

    while (object = buffer.next()) {
        var type = ('nodes_count' in object) ? 'w' : 'n';
        batch.push({
            type: 'put',
            key: type + object.id,
            value: JSON.stringify(object)
        });
    }

    if (batch.length > batchSize) {
        pushBatch(batch, nextBuffer);
    } else {
        nextBuffer();
    }

    count++;
}

function pushBatch(array, callback) {
    db.batch(array, function(err) {
        if (err) return console.log(err);
        batch = [];
        return callback ? callback() : false;
    });
}

nextBuffer();