Well you can always override the toString method of your objects:

    var arr = [
        {name: "Joe", age: 22, toString: function(){return this.name;}},
        {name: "Kevin", age: 24, toString: function(){return this.name;}},
        {name: "Peter", age: 21, toString: function(){return this.name;}}
    ];
         
    var result = arr.join(", ");
    console.log(result);

Since it's not an array you can use map. You need to use a for loop like below:

var classes = {
    'OPEN': 'state_open',
    'COMPLETED': 'state_completed',
    'SKIPPED': 'state_skipped',
    'REJECTED': 'state_rejected'
};

// Create a tmp array for the join
var joined = [];

// Loop over the object Literal.
// the var key is now the prop in the object.
for (var key in classes) {
    var val = classes[key]; // gets the value by looking for the key in the object
    joined.push(val);
}

// Join the array with a space.
joined = joined.join(' ');

Working fiddle

EDIT: accepted answer is better if you want to do it with jQuery, cheers.

You can use Object.values to get an array of the properties of your object, then use the join method of that array to create a string from the values:

var result = users.map(function (a) {
    return Object.values(a).join(', ');
});
console.log(result[0]); // Jon, 34, ES

You can use Array#map method along with Array#join method. Where Array#filter method can be used for filtering non-empty and defined property values.

function obsKeysToString(o, k, sep) {
 // iterate over key array
 return k.map(function(key) {
    // get object property value 
    return o[key];
    // filter out non-empty and defined property
  }).filter(function(v) {
    return v;
    // join the property value array with the separator
  }).join(sep);
}

var keys = ['name', 'description']

var obj = {
  id: 1,
  name: 'Test',
  description: 'Lorem ipsum dolores',
  moreKeysHere: 'moreValues'
}

function obsKeysToString(o, k, sep) {
  return k.map(function(key) {
    return o[key];
  }).filter(function(v) {
    return v;
  }).join(sep);
}

console.log(obsKeysToString(obj, keys, '-'))

Same solution with ES6 arrow function

function obsKeysToString(o, k, sep) {
 return k.map(key => o[key]).filter(v => v).join(sep);
}

var keys = ['name', 'description']

var obj = {
  id: 1,
  name: 'Test',
  description: 'Lorem ipsum dolores',
  moreKeysHere: 'moreValues'
}

function obsKeysToString(o, k, sep) {
  return k.map(key => o[key]).filter(v => v).join(sep);
}
console.log(obsKeysToString(obj, keys, '-'))

Another solution using Array#reduce method.

function obsKeysToString(o, k, sep) {
  // iterate over key array
  return k.reduce(function(str, key) {
    // generate string based on each key
    return str + (o.hasOwnProperty(key) ? (str.length ? sep : '') + o[key] : '');
  }, '')
}

var keys = ['name', 'description']

var obj = {
  id: 1,
  name: 'Test',
  description: 'Lorem ipsum dolores',
  moreKeysHere: 'moreValues'
}

function obsKeysToString(o, k, sep) {
  return k.reduce(function(str, key) {
    return str + (o.hasOwnProperty(key) ? (str.length ? sep : '') + o[key] : '');
  }, '')
}

console.log(obsKeysToString(obj, keys, '-'))

You can try the combination of Object.entries and Array.map

const data = { a: '213', b: 'asv', c: 'sdfs' };
let printData = Object.entries(data).map(entry => entry.join(': ')).join('<br/>');
console.log(printData); // "a: 213<br/>b: asv<br/>c: sdfs"

You have text with line breaks in value. If you print in console theObj.value you will see expected.