simulator of PHP `serialize` function in pure JavaScript

phpSerialize.js

function phpSerialize(obj){ // e.g. a:1{i:2;s:5:"22222";}
    var props = [];
    for(var prop in obj)
        props.push(_phpSerializeVar(prop)+_phpSerializeVar(obj[prop]));
    return 'a:'+props.length+':{'+props.join('')+'}';
}
function _phpSerializeVar(prop){ // e.g. i:2; e.g. s:5:"22222";
    return (isNaN(prop) && prop.length) ?
        's:' + prop.length + ':"' + prop + '";' :
        'i:' + prop + ';' ;
}

console.log(phpSerialize({2: 123, '8': 'test', 'field':'value'}));