How to simplify multiple if statements javascript?

My idea is：

var icons = {
    a: 'a.png',
    b: 'b.png',
    c: 'c.png',
    d: 'd.png',
}

if (date != -1) {
    Object.keys(icons).forEach(function(key) {
        if (data[key]) {
            //Add icon icons[key]
        }
    });
}

var statusColors = {
    active: 'Green',
    onhold: 'Yellow',
    inactive: 'Grey',
}

//Background statusColors[status]

I think it is pretty good as it is. Is is better to have understandable code than complex code that does exactly the same thing.

You don't have to do

if (a === true)

as it's equivalent to

if ( a )

There is no way to "simplify" it, but you can try to use switch statement instead:

switch (status) {
  case 'active':
    // active
    break;
  case 'onhold':
    // onhold
    break;
  case 'inactive':
    // inactive
    break;
  default:
    console.log('default');
}

You can even "group" some conditions:

switch (status) {
  case 'active':
  case 'onhold':
    // active AND onhold case
    break;
  case 'inactive':
    // inactive
    break;
  default:
    console.log('default');
}

More about switch statement -> https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Statements/switch

For Status variable you can use switch but for the first condition you have to use if-else statements I think.

switch (status) {
        case "active":
            //Background Green
            break;
        case "onhold":
            //Background Yellow
            break;
        case "inactive":
            //Background Red
            break;
        default:
            //Backgeound Grey
    }

Your question doesn't quite give the details of the actions in each case, but if they're very similar, and there's a match between the property name and whatever action you need to take, you can use loops.

['a','b','c','d'].forEach(function (k)
{
    if (objectFromJSON[k])
    {
       addIcon(k);
    }
});

For the second part, it's slightly more complex as you have status names that don't match the color. You can either:

• define CSS classes with those status names, and use the status name to set the class:

  CSS:

  .status-active
  {
      background: green;
  }
  .status-onhold
  {
      background: yellow;
  }
  .status-inactive
  {
      background: red;
  }
  

  JS:

  theHTMLobject.classList.addClass('status-'+objectFromJSON.status);
  

• use an object's properties (or a Map) to convert the status into a color

Do you mean "simplify" or do you mean "shorten" - because the two are almost mutually exclusive (shorter code is often not simpler!)

Your code is clear, and understandable. But it is a bit verbose, and can get much more complex as things grow. Sometimes it is better to shorten and the risk of making it a bit harder to understand.

You could consider things like a map between the status and the appropriate color

var backgroundStatusMap = {
    "active":"green",
    "onhold": "yellow",
    "inactive": "red"
};

var backgroundColor = backgroundStatusMap[json.status];

Things like this can be added to easier if you as add new statuses - without having to trawl for the right place to put a new if.. condition.

Similarly, you could create a map for the booleans-to-icons

var iconMap = {
    "a":"icon_a.png",
    "b": "icon_b.png"
};

function getIcon(json, prop){
    if(json[prop])
      return iconMap[prop];
    return null;
}

var iconA = getIcon(json,"a");
var iconB = getIcon(json,"b");

a?setIconA():b?setIconB:c?setIconC;d?setIconD

and

status == "active" ? setGreen() : status == "onhold": setYellow()

and so on.