Javascript inline replace undefined with empty string - Stack Overflow

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I have this function:

function callWS(input) {
    var output = {
        "type"  : input["type"]  || "",
        "mark"  : input["mark"]  || "",
        "model" : input["model"] || "",
        "year"  : input["year"]  || ""
    };

    return output;
}

I want the user to call this function in many ways:

callWS(); ==> {"type":"","mark":"","model":"","year":""}
callWS({"type":"moto"}); ==> {"type":"moto","mark":"","model":"","year":""}
callWS({"type":"moto","mark":"audi"}); ==> {"type":"moto","mark":"audi","model":"","year":""}

And in case a parameters is undefined, to initialize it as an empty string. Currently my function does not work in the first case, but in the other is working.

When I call it like callWS() I get:

Uncaught TypeError: Cannot read property 'type' of undefined

To be honest I don't know why it works for the 2 and 3 case but I need to make it work for the first case also. I know that if I use:

if (input["type"])

will do the trick but I need an inline solution. Is this possible somehow?

I have this function:

function callWS(input) {
    var output = {
        "type"  : input["type"]  || "",
        "mark"  : input["mark"]  || "",
        "model" : input["model"] || "",
        "year"  : input["year"]  || ""
    };

    return output;
}

I want the user to call this function in many ways:

callWS(); ==> {"type":"","mark":"","model":"","year":""}
callWS({"type":"moto"}); ==> {"type":"moto","mark":"","model":"","year":""}
callWS({"type":"moto","mark":"audi"}); ==> {"type":"moto","mark":"audi","model":"","year":""}

And in case a parameters is undefined, to initialize it as an empty string. Currently my function does not work in the first case, but in the other is working.

When I call it like callWS() I get:

Uncaught TypeError: Cannot read property 'type' of undefined

To be honest I don't know why it works for the 2 and 3 case but I need to make it work for the first case also. I know that if I use:

if (input["type"])

will do the trick but I need an inline solution. Is this possible somehow?

• javascript
• string
• undefined
• ternary-operator

Share Improve this question Follow asked Dec 13, 2016 at 16:33 paulalexandrupaulalexandru 9,53077 gold badges6767 silver badges9696 bronze badges 6

• 4 You have to supply input itself with default value too. Just add input = input || {} to the beginning of callWS – hindmost Commented Dec 13, 2016 at 16:36
• 1 Define your function as function callWS(input = {}). – user663031 Commented Dec 13, 2016 at 16:38
• @torazaburo - the project does not include ES6 – paulalexandru Commented Dec 13, 2016 at 16:39
• @François Wahl - Unfortunately the project does not use jQuery, it doesn't use any external library. – paulalexandru Commented Dec 13, 2016 at 16:51
• @paulalexandru hence the part, if you are not using jQuery you can write your own easily :) I only used JavaScript in my example too but you already have it sorted anyway :) – Nope Commented Dec 13, 2016 at 16:54

 |  Show 1 more ment

3 Answers 3

Sorted by: Reset to default 5

You have to supply input variable itself with default value too.

function callWS(input) {
   input = input || {};
   ...
}

Otherwise you access properties on unexisting (undefined) object which lead to error (what you have now).

On other hand accessing unexisting properties on existing object isn't treated as error in JS.

You can write your own extend method and use that. That way you can have a default object, giving it which ever default values and then merge it with the object passed into the function.

function extend(a, b){
    for(var key in b){
        if(b.hasOwnProperty(key)){
            a[key] = b[key];
        }
    }

    return a;
}

function callWS(input) {
    var defaultInput = {
        "type": "",
        "mark": "",
        "model":"",
        "year": ""
    }
    
    var output = extend(defaultInput, input);

    return output;
}

console.log(callWS());
console.log(callWS({"type":"moto"}));
console.log(callWS({"type":"moto","mark":"audi"}));

In ES6, write this as

function callWS({type = "", mark = "", model = "", year = ""} = {}) {
  return {type, mark, model, year};
}

Here's another approach not involving ES6. Many libraries contain a default utility, which will apply some properties to another object if they are missing.

function deflt(obj, defaults) {
  var keys = Object.keys(defaults);
  for (var i = 0; i < keys.length: i++) {
    var key = keys[i];
    if (!(key in obj)) obj[key] = defaults[key];
  }
  return obj;
}

You can use this as follows:

function callWS(input) {
  input = input || {};
  deflt(input, {type: "", mark: "", model: "", year: ""});
  return input;
}

Note: as written this will return a modified version of the input. Adjust as necessary if this is not what you want.

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