var foo = {"bar": "123"};
...
foo.bar = parseInt(foo.bar); // (int) 123

var int = +string;

var string = otherType + "";
var bool = !!anything;

foo.bar = Number(foo.bar);

$foo->bar = (int)$foo->bar;
print('var foo = ' . json_encode($foo));

parseInt('010', 10); // 10

var i = "123";
i = new Number(i); // Number numeric wrapper
var j = "123";
j = Number(j); // Number primitive

("78.5" | 0) //bitwise or forces the string to parse as int

var toNumber = function (input) {
    if ( typeof input !== "string" ) throw "Not a string";

    var length = input.length;
    if ( length === 0 ) return;
    var c1 = input.charCodeAt(0);

    if ( c1 === 45 || c1 === 43 ){
        if ( length === 1 ) return;
        var start = 1;
    } else {
        var start = 0;
    }

    var out = 0, c;
    while( start < length && input.charCodeAt(start) === 48 ) start++;

    for ( ; start < length; start++){
        c = input.charCodeAt(start) ^ 48;
        if ( c > 9 ) return;
        out = (out * 10) + c;
    }

    if ( c1 === 45 ) return out * -1;
    return out;
}