Convert letters to digits using "old" phone keybord

lettersToDigits.js

var _in = 'erwan123';
var _out = [];

var map = ['0 ','1','2abc','3def','4ghi','5jkl','6mno','7pqrs','8tuv','9wxyz'];
for(var i = 0; i < _in.length; i++)
{
    for (var j = 0; j < map.length; j++)
    {
        if (map[j] && map[j].indexOf(_in[i]) > -1)
        {
            _out.push(j);
            break;
        }
    }
}
console.log(_out.join('')); // output 37926123