check and initialize a variable at the same time in livescript

how to do it in livescript

scope = {};

objs = [
    {type:'aaa', val:'foo1'},
    {type:'bbb', val:'foo2'},
    {type:'ccc', val:'foo3'},
    {type:'aaa', val:'foo4'},
    {type:'bbb', val:'foo5'},
    {type:'ccc', val:'foo6'}
];

objs.forEach(function(obj) {

    /* UGLY!! how do we avoid this kind of existence-checking-and-initialization */
    if !scope[obj.type] {
        scope[obj.type] = []
    }

    scope[obj.type].push(obj.name);
})

from clkao: scope[obj.type] ?= []