How to get value from Object, with default value

Question

I constantly find myself passing config values to functions accessing them like this:

var arg1 = 'test1';
if(isUndefined(config.args.arg1)){
  arg1 = config.args.arg1;
} 

var arg2 = 'param2';
if(isUndefined(config.args.arg2)){
  arg2 = config.args.arg2;
} 

var arg3 = '123';
if(isUndefined(config.args.arg3)){
  arg3 = config.args.arg3;
} 

where I later use them like this:

var url = '<some-url>?id='+arg1+'&='+arg2 +'=' + arg3;

Does jQuery/ExtJS or any other framework provide a solution to access variables like this in a simple way, and give variables a default value?

Something like:

getValueOfObject(config,'args.arg3','<default>');

Or is there maybe a standard solution for this.

NOTE:

I was also thinking about the common pattern where you have defaults

var defaults = {
   args: {
      args1: ....
   }
   ...
}

and doing an object merge.

And then encoding the object to a param String. But as you can see the object values also sometimes contain parameter names.

Answer 1

Generally, one can use the or operator to assign a default when some variable evaluates to falsy:

var foo = couldBeUndefined || "some default";

so:

var arg1 = config.args.arg1 || "test";
var arg2 = config.args.arg2 || "param2";

assuming that config.args is always defined, as your example code implies.

Answer 2

看起来lodash终于有了_.get()函数！

Answer 3

With ES2018, you can now write options = { ...defaults, ...options } :

Spread syntax - JavaScript | MDN

Shallow-cloning (excluding prototype) or merging of objects is now possible using a shorter syntax than Object.assign() .

 const obj1 = { foo: 'bar', x: 42 }; const obj2 = { foo: 'baz', y: 13 }; const clonedObj = { ...obj1 }; // Object { foo: "bar", x: 42 } const mergedObj = { ...obj1, ...obj2 }; // Object { foo: "baz", x: 42, y: 13 }

Answer 4

try var options = extend(defaults, userOptions);

This way you get all the userOptions and fall back to defaults when they don't pass any options.

Note use any extend implementation you want.

Answer 5

With ECMAScript 2020 it may be safer to use Nullish coalescing operator .

let foo = obj.maybeUndefined ?? "default value";

JS treats 0, -0, null, false, NaN, undefined, or the empty string ("") as falsy . So, using or operator for setting a default value in the following example may cause unexpected results

let obj = { maybeUndefined: 0 };
let foo = obj.maybeUndefined || 1; // foo == 1

Here, foo becomes equal to 1 , when maybeUndefined is actually defined. If foo should be assigned a default value only when maybeUndefined is actually undefined or null , then we can use Nullish coalescing operator .

let obj = { maybeUndefined: 0 };
let foo = obj.maybeUndefined ?? 1; // foo == 0

let obj = {};
let foo = obj.maybeUndefined ?? 1; // foo == 1