CODEWITHSUNDEEP
javascriptarraysfunction
Mr.Web
Mr.Web

Reputation: 7144

Javascript default array/object parameter value

I'm making up a way of setting function array parameter to a default value (one ES5 not new ES6/2015).

My first idea was this:

window.fnc = function(args){
    defaults = {
        height: 120,
        width: 32
    }

    args = args || defaults;

    console.log(args['height']+'x'+args['width'])

}

and will be used like this:

fnc({height:45, width:12}); //Result: 45x12

or

fnc(); //Result: 120x32

This works ok. But of course at line #7 the args is replaced by defaults or it is not, so if either one of the 2 values are missing i get an undefined.

fnc({height:45}); //Result: 45xundefined

How do I go about this?

Upvotes: 1

Views: 95

Answers (2)

anotherdev
anotherdev

Reputation: 2569

You can iterate the keys of default to copy the one missing in args.

window.fnc = function(args){
    defaults = {
        height: 120,
        width: 32
    }

    //args = args || defaults;
    if(args == null)
      args = defaults;
    else {
      for(var i in defaults) {
        if(args[i] == null) args[i] = defaults[i];
      }
    }

    console.log(args['height']+'x'+args['width'])

}

If you have sub-objects in defaults, you will need to do a recursive function.

EDIT:

Recursive example:

// check if obj is an object
function isObject(obj) {
  return typeof obj == "object";
}
// check if obj is an array
function isArray(obj) {
  return (typeof obj == "object") && (Object.getPrototypeOf( obj ) === Array.prototype);
}
// copy the attributes from original into dest
function copy_attributes(original, dest) {

  for(var i in original) {

    if(isArray(original[i])) {

      dest[i] = JSON.parse(JSON.stringify(original[i])); // copy
    }
    else if(isObject(original[i])) {

      copy_attributes(original[i], dest[i]);
    }
    else {

      dest[i] = JSON.parse(JSON.stringify(original[i])); // copy
    }
  }
};

Upvotes: 2

Sebass van Boxel
Sebass van Boxel

Reputation: 2602

I use this code snippet from time to time:

 args = args || defaults;
     for (var opt in defaults) {
        if (defaults.hasOwnProperty(opt) && !args.hasOwnProperty(opt)) {
            args[opt] = defaults[opt];
        }
    }

Basically you iterate over all the values from the default arguments (for (var opt...) and check against the values of the arguments whether it is missing or not. (if (defaults.has...). If it is missing, add the default value (args[opt] =...).

(I think I even found this snippet on SA, but not sure. Will add a link to the original answer if so.)

Upvotes: 3

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