Actually, the best solution is using JSON:

Documentation

JSON.parse(text[, reviver]);

Examples:

1)

var myobj = JSON.parse('{ "hello":"world" }');
alert(myobj.hello); // 'world'

2)

var myobj = JSON.parse(JSON.stringify({
    hello: "world"
});
alert(myobj.hello); // 'world'

3) Passing a function to JSON

var obj = {
    hello: "World",
    sayHello: (function() {
        console.log("I say Hello!");
    }).toString()
};
var myobj = JSON.parse(JSON.stringify(obj));
myobj.sayHello = new Function("return ("+myobj.sayHello+")")();
myobj.sayHello();

Your string looks like a JSON string without the curly braces.

This should work then:

obj = eval('({' + str + '})');

If I'm understanding correctly:

var properties = string.split(', ');
var obj = {};
properties.forEach(function(property) {
    var tup = property.split(':');
    obj[tup[0]] = tup[1];
});

I'm assuming that the property name is to the left of the colon and the string value that it takes on is to the right.

Note that Array.forEach is JavaScript 1.6 -- you may want to use a toolkit for maximum compatibility.

This simple way...

var string = "{firstName:'name1', lastName:'last1'}";
eval('var obj='+string);
alert(obj.firstName);

output

name1

Since JSON.parse() method requires the Object keys to be enclosed within quotes for it to work correctly, we would first have to convert the string into a JSON formatted string before calling JSON.parse() method.

var obj = '{ firstName:"John", lastName:"Doe" }';

var jsonStr = obj.replace(/(\w+:)|(\w+ :)/g, function(matchedStr) {
  return '"' + matchedStr.substring(0, matchedStr.length - 1) + '":';
});

obj = JSON.parse(jsonStr); //converts to a regular object

console.log(obj.firstName); // expected output: John
console.log(obj.lastName); // expected output: Doe

This would work even if the string has a complex object (like the following) and it would still convert correctly. Just make sure that the string itself is enclosed within single quotes.

var strObj = '{ name:"John Doe", age:33, favorites:{ sports:["hoops", "baseball"], movies:["star wars", "taxi driver"]  }}';

var jsonStr = strObj.replace(/(\w+:)|(\w+ :)/g, function(s) {
  return '"' + s.substring(0, s.length-1) + '":';
});

var obj = JSON.parse(jsonStr);
console.log(obj.favorites.movies[0]); // expected output: star wars

If you have a string like foo: 1, bar: 2 you can convert it to a valid obj with:

str
  .split(',')
  .map(x => x.split(':').map(y => y.trim()))
  .reduce((a, x) => {
    a[x[0]] = x[1];
    return a;
  }, {});

Thanks to niggler in #javascript for that.

Update with explanations:

const obj = 'foo: 1, bar: 2'
  .split(',') // split into ['foo: 1', 'bar: 2']
  .map(keyVal => { // go over each keyVal value in that array
    return keyVal
      .split(':') // split into ['foo', '1'] and on the next loop ['bar', '2']
      .map(_ => _.trim()) // loop over each value in each array and make sure it doesn't have trailing whitespace, the _ is irrelavent because i'm too lazy to think of a good var name for this
  })
  .reduce((accumulator, currentValue) => { // reduce() takes a func and a beginning object, we're making a fresh object
    accumulator[currentValue[0]] = currentValue[1]
    // accumulator starts at the beginning obj, in our case {}, and "accumulates" values to it
    // since reduce() works like map() in the sense it iterates over an array, and it can be chained upon things like map(),
    // first time through it would say "okay accumulator, accumulate currentValue[0] (which is 'foo') = currentValue[1] (which is '1')
    // so first time reduce runs, it starts with empty object {} and assigns {foo: '1'} to it
    // second time through, it "accumulates" {bar: '2'} to it. so now we have {foo: '1', bar: '2'}
    return accumulator
  }, {}) // when there are no more things in the array to iterate over, it returns the accumulated stuff

console.log(obj)

Confusing MDN docs:

Demo:

Function:

const str2obj = str => {
  return str
    .split(',')
    .map(keyVal => {
      return keyVal
        .split(':')
        .map(_ => _.trim())
    })
    .reduce((accumulator, currentValue) => {
      accumulator[currentValue[0]] = currentValue[1]
      return accumulator
    }, {})
}

console.log(str2obj('foo: 1, bar: 2')) // see? works!

You need use JSON.parse() for convert String into a Object:

var obj = JSON.parse('{ "firstName":"name1", "lastName": "last1" }');

if you're using JQuery:

var obj = jQuery.parseJSON('{"path":"/img/filename.jpg"}');
console.log(obj.path); // will print /img/filename.jpg

REMEMBER: eval is evil! :D

I implemented a solution in a few lines of code which works quite reliably.

Having an HTML element like this where I want to pass custom options:

<div class="my-element"
    data-options="background-color: #dadada; custom-key: custom-value;">
</div>

a function parses the custom options and return an object to use that somewhere:

function readCustomOptions($elem){
    var i, len, option, options, optionsObject = {};

    options = $elem.data('options');
    options = (options || '').replace(/\s/g,'').split(';');
    for (i = 0, len = options.length - 1; i < len; i++){
        option = options[i].split(':');
        optionsObject[option[0]] = option[1];
    }
    return optionsObject;
}

console.log(readCustomOptions($('.my-element')));

string = "firstName:name1, lastName:last1";

This will work:

var fields = string.split(', '),
    fieldObject = {};

if( typeof fields === 'object') ){
   fields.each(function(field) {
      var c = property.split(':');
      fieldObject[c[0]] = c[1];
   });
}

However it's not efficient. What happens when you have something like this:

string = "firstName:name1, lastName:last1, profileUrl:";

split() will split 'http'. So i suggest you use a special delimiter like pipe

 string = "firstName|name1, lastName|last1";


   var fields = string.split(', '),
        fieldObject = {};

    if( typeof fields === 'object') ){
       fields.each(function(field) {
          var c = property.split('|');
          fieldObject[c[0]] = c[1];
       });
    }

I'm using JSON5, and it's works pretty well.

The good part is it contains no eval and no new Function, very safe to use.