SOURCE

// var str = "hello world";
function test(str) {
var a = str.replace(/\s/,"");
var b = a.split("");
var c = Array.from(new Set(b));
let temp = [];
c.map((item,index)=>{
let num = 0;
let Index = b.indexOf(item);
b.forEach(Item=>{
if (Index !== -1) {
    num++;
    Index = b.indexOf(item, Index + 1)
} else {
    return false;
}
})
let obj= "{"+item+":"+num+"}"
temp.push(obj);
})
console.log(temp)
}
// test("hello world");
test.apply(this,["hello world"])